Descripción: The pro-opiomelanocortin (POMC) gene is expressed in a subset of hypothalamic and hindbrain neurons and in pituitary melanotrophs and corticotrophs. POMC neurons release the potent opioid β-endorphin and several active melanocortins that control homeostasis and feeding behavior. POMC gene expression in the CNS is believed to be controlled by distinct cis- acting regulatory sequences. To analyze the transcriptional regulation of POMC in neuronal and endocrine cells, we produced transgenic mice carrying POMC27*, a transgene containing the entire 6 kb of the POMC transcriptional unit together with 13 kb of 5' flanking regions and 8 kb of 3' flanking regions: POMC27* was tagged with a heterologous 30 bp oligonucleotide in the third exon. In situ hybridization studies showed an accurate cell-specific pattern of expression of POMC27* in the arcuate nucleus and the pituitary. Hypothalamic mRNA-positive neurons colocalized entirely with β-endorphin immunoreactivity. No ectopic transgenic expression was detected in the brain. Deletional analyses demonstrated that neuron-specific expression of POMC transgenes required distal 5' sequences localized upstream of the pituitary- responsive proximal cis-acting elements that were identified previously. POMC27* exhibited a spatial and temporal pattern of expression throughout development that exactly paralleled endogenous POMC. RNase protection assays revealed that POMC27* expression mimicked that of POMC in different areas of the CNS and most peripheral organs with no detectable ectopic expression. Hormonal regulation of POMC27* and POMC was identical in the hypothalamus and pituitary. These results show that distal 5' sequences of the POMC gene located between -13 and -2 kb target expression into the CNS of transgenic mice in a precise neuron-specific, developmentally and hormonally regulated manner.

Descripción: This paper reviews basic concepts of modern molecular biology with the premise that its influence in today's medicine is so important that its knowledge cannot remain limited to a few experts. I first analyze the overall structure and organization of human genes, their split nature and the flow of genetic information from DNA to protein. The role of transcriptional control in the regulation of gene expression and cell differentiation is described by introducing experimental examples that define the importance of "master" genes. Basic concepts of genetic engineering, the generation of transgenic and knock out animals and the uses of molecular biology in clinical diagnosis, paternity tests and forensic medicine are presented. Finally, I discuss the possibilities of gene therapy and the fantasies and realities of transgenesis and cloning by nuclear transplant in humans.

Descripción: Extracellular signal-regulated protein kinase 1 and 2 (ERK1/2) are members of the MAPK family and participate in the transduction of stimuli in cellular responses. Their long-term actions are accomplished by promoting the expression of specific genes whereas faster responses are achieved by direct phosphorylation of downstream effectors located throughout the cell. In this study we determined that hERK1 translocates to the mitochondria of HeLa cells upon a proliferative stimulus. In the mitochondrial environment, hERK1 physically associates with (i) at least 5 mitochondrial proteins with functions related to transport (i.e. VDAC1), signalling, and metabolism; (ii) histones H2A and H4; and (iii) other cytosolic proteins. This work indicates for the first time the presence of diverse ERK-complexes in mitochondria and thus provides a new perspective for assessing the functions of ERK1 in the regulation of cellular signalling and trafficking in HeLa cells. © 2009 Galli et al.

Descripción: The wheat spikelet meristem differentiates into up to 12 floret primordia, but many of them fail to reach the fertile floret stage at anthesis. We combined microarray, biochemical and anatomical studies to investigate floret development in wheat plants grown in the field under short or long days (short days extended with low-fluence light) after all the spikelets had already differentiated. Long days accelerated spike and floret development and greening, and the expression of genes involved in photosynthesis, photoprotection and carbohydrate metabolism. These changes started while the spike was in the light-depleted environment created by the surrounding leaf sheaths. Cell division ceased in the tissues of distal florets, which interrupted their normal developmental progression and initiated autophagy, thus decreasing the number of fertile florets at anthesis. A massive decrease in the expression of genes involved in cell proliferation, a decrease in soluble carbohydrate levels, and an increase in the expression of genes involved in programmed cell death accompanied anatomical signs of cell death, and these effects were stronger under long days. We propose a model in which developmentally generated sugar starvation triggers floret autophagy, and long days intensify these processes due to the increased carbohydrate consumption caused by the accelerated plant development. © 2008 The Authors.

Descripción: The Saccharomyces cerevisiae UGA4 gene, which encodes the γ-aminobutyric acid (GABA) and δ-aminolaevulinic acid (ALA) permease, is well known to be regulated by the nitrogen source. Its expression levels are low in the presence of a rich nitrogen source but are higher when a poor nitrogen source is used. In addition, GABA can induce UGA4 expression when cells are grown with proline but not when they are grown with ammonium. Although vast amounts of evidence have been gathered about UGA4 regulation by nitrogen, little is known about its regulation by the carbon source. Using glucose and acetate as rich and poor carbon source respectively, this work aimed to shed light on hitherto unclear aspects of the regulation of this gene. In poor nitrogen conditions, cells grown with acetate were found to have higher UGA4 basal expression levels than those grown with glucose, and did not show UGA4 induction in response to GABA. Analysis of the expression and subcellular localization of the transcription factors that regulate UGA4 as well as partial deletions and site-directed mutations of the UGA4 promoter region suggested that there are two parallel pathways that act in regulating this gene by the carbon source. Furthermore, the results demonstrate the existence of a new factor operating in UGA4 regulation. © 2007 SGM.

Descripción: The role of GAs in promoting seed germination is well known and experiments with seeds from different species have suggested the requirement of de novo synthesis of GAs upon imbibition for germination. There are also strong indications that the enhancement of GA synthesis is part of the mechanism through which environmental signals (i.e. light) induce germination. Since along the GA biosynthetic pathway, oxidation at C-20 carried out by GA 20-oxidases is thought to be a site of regulation, a cDNA clone encoding a GA 20-oxidase was isolated from embryos of sorghum (SbGA 20ox). Expression analysis of this gene in embryos within imbibed caryopses with low dormancy showed detectable amounts of the specific mRNA early upon incubation, increasing thereafter. In contrast, it remained barely detectable in embryos from dormant caryopses. Changes in endogenous GA4 levels were in agreement with those of SbGA 20ox mRNA, suggesting that GA production might be regulated differentially at the level of transcription of this gene. The expression of SbGA 20ox was enhanced in incubated embryos isolated from either type of caryopses, illustrating a physiological control exerted by the surrounding seed tissues on gene expression. The results also show that ABA leads to a suppression of transcription of this gene.

Descripción: Expression of lysP, which encodes the lysine-specific transporter LysP in Escherichia coli, is regulated by the concentration of exogenous available lysine. In this study, the LysR-type transcriptional regulator ArgP was identified as the activator of lysP expression. At lysine concentrations higher than 25 μM, lysP expression was shut off and phenocopied an argP deletion mutant. Purified ArgP-His 6 bound to the lysP promoter/control region at a sequence containing a conserved T-N 11-A motif. Its affinity increased in the presence of lysine but not in the presence of the other known coeffector, arginine. In vivo data suggest that lysine-loaded ArgP and arginine-loaded ArgP compete at the lysP promoter. We propose that lysine-loaded ArgP prevents lysP transcription at the promoter clearance step, as described for the lysine-dependent regulation of argO (R. S. Laishram and J. Gowrishankar, Genes Dev. 21:1258-1272, 2007). The global regulator Lrp also bound to the lysP promoter/control region. An lrp mutant exhibited reduced lysP expression in the absence of external lysine. These results indicate that ArgP is a major regulator of lysP expression but that Lrp modulates lysP transcription under lysine-limiting conditions. © 2011, American Society for Microbiology.

Descripción: The first specific precursor of porphyrin biosynthesis is δ-aminolevulinic acid. δ-Aminolevulinic acid enters Saccharomyces cerevisiae cells through the γ-aminobutyric acid specific permease Uga4p. It was described that this permease is inducible by γ-aminobutyric acid and its regulation involves several specific and pleiotropic transcriptional factors. However, some studies showed that under certain growth conditions the synthesis of Uga4p was not dependent on the presence of γ-aminobutyric acid. To study the effect of the trans-acting factors Uga43p, Uga3p, Uga35p, Ure2p and Gln3p on the expression of UGA4, we measured γ-aminobutyric acid and δ-aminolevulinic acid uptake in yeast mutant cells, lacking one of these regulatory factors, grown under different conditions. Experiments analyzing the UGA4 promoter using a fusion construction UGA4::lacZ were also carried out. The results show that the constitutive expression of the UGA4 gene found in cells under certain growth conditions depends on the presence of Uga3p and Uga35p. In contrast, Gln3p and Ure2p do not seem to have any effect on this constitutive mechanism. Copyright (C) 2000 Federation of European Microbiological Societies.

Descripción: Background: Subtractive hybridization methods are valuable tools for identifying differentially regulated genes in a given tissue avoiding redundant sequencing of clones representing the same expressed genes, maximizing detection of low abundant transcripts and thus, affecting the efficiency and cost effectiveness of small scale cDNA sequencing projects aimed to the specific identification of useful genes for breeding purposes. The objective of this work is to evaluate alternative strategies to high-throughput sequencing projects for the identification of novel genes differentially expressed in sunflower as a source of organ-specific genetic markers that can be functionally associated to important traits. Results: Differential organ-specific ESTs were generated from leaf, stem, root and flower bud at two developmental stages (R1 and R4). The use of different sources of RNA as tester and driver cDNA for the construction of differential libraries was evaluated as a tool for detection of rare or low abundant transcripts. Organ-specificity ranged from 75 to 100% of non-redundant sequences in the different cDNA libraries. Sequence redundancy varied according to the target and driver cDNA used in each case. The R4 flower cDNA library was the less redundant library with 62% of unique sequences. Out of a total of 919 sequences that were edited and annotated, 318 were non-redundant sequences. Comparison against sequences in public databases showed that 60% of non-redundant sequences showed significant similarity to known sequences. The number of predicted novel genes varied among the different cDNA libraries, ranging from 56% in the R4 flower to 16 % in the R1 flower bud library. Comparison with sunflower ESTs on public databases showed that 197 of non-redundant sequences (60%) did not exhibit significant similarity to previously reported sunflower ESTs. This approach helped to successfully isolate a significant number of new reported sequences putatively related to responses to important agronomic traits and key regulatory and physiological genes. Conclusions: The application of suppressed subtracted hybridization technology not only enabled the cost effective isolation of differentially expressed sequences but it also allowed the identification of novel sequences in sunflower from a relative small number of analyzed sequences when compared to major sequencing projects. © 2003 Fernández et al; licensee BioMed Central Ltd.

Descripción: To understand how the Rhizobium leguminosarum rail-raiR quorum-sensing system is regulated, we identified mutants with decreased levels of RaiI-made N-acyl homoserine lactones (AHLs). A LuxR-type regulator, ExpR, is required for raiR expression, and RaiR is required to induce rail. Since raiR (and rail) expression is also reduced in cinI and cinR quorum-sensing mutants, we thought CinI-made AHLs may activate ExpR to induce raiR. However, added CinI-made AHLs did not induce raiR expression in a cinI mutant. The reduced raiR expression in cinI and cinR mutants was due to lack of expression of cinS immediately downstream of cinI. cinS encodes a 67-residue protein, translationally coupled to CinI, and cinS acts downstream of expR for raiR induction. Cloned cinS in R. leguminosarum caused an unusual collapse of colony structure, and this was delayed by mutation of expR. The phenotype looked like a loss of exopolysaccharide (EPS) integrity; mutations in cinI, cinR, cinS, and expR all reduced expression of plyB, encoding an EPS glycanase, and mutation of plyB abolished the effect of cloned cinS on colony morphology. We conclude that CinS and ExpR act to increase PlyB levels, thereby influencing the bacterial surface. CinS is conserved in other rhizobia, including Rhizobium etli; the previously observed effect of cinI and cinR mutations decreasing swarming in that strain is primarily due to a lack of CinS rather than a lack of CinI-made AHL. We conclude that CinS mediates quorum-sensing regulation because it is coregulated with an AHL synthase and demonstrate that its regulatory effects can occur in the absence of AHLs. Copyright © 2009, American Society for Microbiology.

Descripción: The placenta produces a wide number of molecules that play essential roles in the establishment and maintenance of pregnancy. In this context, leptin has emerged as an important player in reproduction. The synthesis of leptin in normal trophoblastic cells is regulated by different endogenous biochemical agents, but the regulation of placental leptin expression is still poorly understood. We have previously reported that 17β-estradiol (E 2) up-regulates placental leptin expression. To improve the understanding of estrogen receptor mechanisms in regulating leptin gene expression, in the current study we examined the effect of membrane-constrained E 2 conjugate, E-BSA, on leptin expression in human placental cells. We have found that leptin expression was induced by E-BSA both in BeWo cells and human placental explants, suggesting that E 2 also exerts its effects through membrane receptors. Moreover E-BSA rapidly activated different MAPKs and AKT pathways, and these pathways were involved in E 2 induced placental leptin expression. On the other hand we demonstrated the presence of ERα associated to the plasma membrane of BeWo cells. We showed that E 2 genomic and nongenomic actions could be mediated by ERα. Supporting this idea, the downregulation of ERα level through a specific siRNA, decreased E-BSA effects on leptin expression. Taken together, these results provide new evidence of the mechanisms whereby E 2 regulates leptin expression in placenta and support the importance of leptin in placental physiology. © 2012 Elsevier B.V..

Descripción: The proopiomelanocortin gene (POMC) is expressed in a group of neurons present in the arcuate nucleus of the hypothalamus. Neuron-specific POMC expression in mammals is conveyed by two distal enhancers, named nPE1 and nPE2. Previous transgenic mouse studies showed that nPE1 and nPE2 independently drive reporter gene expression to POMC neurons. Here, we investigated the evolutionary mechanisms that shaped not one but two neuron- specific POMC enhancers and tested whether nPE1 and nPE2 drive identical or complementary spatiotemporal expression patterns. Sequence comparison among representative genomes of most vertebrate classes and mammalian orders showed that nPE1 is a placental novelty. Using in silico paleogenomics we found that nPE1 originated from the exaptation of a mammalian- apparent LTR retrotransposon sometime between the metatherian/ eutherian split (147 Mya) and the placental mammal radiation (≈90 Mya). Thus, the evolutionary origin of nPE1 differs, in kind and time, from that previously demonstrated for nPE2, which was exapted from a CORE-short interspersed nucleotide element (SINE) retroposon before the origin of prototherians, 166 Mya. Transgenic mice expressing the fluorescent markers tomato and EGFP driven by nPE1 or nPE2, respectively, demonstrated coexpression of both reporter genes along the entire arcuate nucleus. The onset of reporter gene expression guided by nPE1 and nPE2 was also identical and coincidental with the onset of Pomc expression in the presumptive mouse diencephalon. Thus, the independent exaptation of two unrelated retroposons into functional analogs regulating neuronal POMC expression constitutes an authentic example of convergent molecular evolution of cell-specific enhancers.

Descripción: Background. Considering that sunflower production is expanding to arid regions, tolerance to abiotic stresses as drought, low temperatures and salinity arises as one of the main constrains nowadays. Differential organ-specific sunflower ESTs (expressed sequence tags) were previously generated by a subtractive hybridization method that included a considerable number of putative abiotic stress associated sequences. The objective of this work is to analyze concerted gene expression profiles of organ-specific ESTs by fluorescence microarray assay, in response to high sodium chloride concentration and chilling treatments with the aim to identify and follow up candidate genes for early responses to abiotic stress in sunflower. Results. Abiotic-related expressed genes were the target of this characterization through a gene expression analysis using an organ-specific cDNA fluorescence microarray approach in response to high salinity and low temperatures. The experiment included three independent replicates from leaf samples. We analyzed 317 unigenes previously isolated from differential organ-specific cDNA libraries from leaf, stem and flower at R1 and R4 developmental stage. A statistical analysis based on mean comparison by ANOVA and ordination by Principal Component Analysis allowed the detection of 80 candidate genes for either salinity and/or chilling stresses. Out of them, 50 genes were up or down regulated under both stresses, supporting common regulatory mechanisms and general responses to chilling and salinity. Interestingly 15 and 12 sequences were up regulated or down regulated specifically in one stress but not in the other, respectively. These genes are potentially involved in different regulatory mechanisms including transcription/translation/protein degradation/protein folding/ROS production or ROS-scavenging. Differential gene expression patterns were confirmed by qRT-PCR for 12.5% of the microarray candidate sequences. Conclusion. Eighty genes isolated from organ-specific cDNA libraries were identified as candidate genes for sunflower early response to low temperatures and salinity. Microarray profiling of chilling and NaCl-treated sunflower leaves revealed dynamic changes in transcript abundance, including transcription factors, defense/stress related proteins, and effectors of homeostasis, all of which highlight the complexity of both stress responses. This study not only allowed the identification of common transcriptional changes to both stress conditions but also lead to the detection of stress-specific genes not previously reported in sunflower. This is the first organ-specific cDNA fluorescence microarray study addressing a simultaneous evaluation of concerted transcriptional changes in response to chilling and salinity stress in cultivated sunflower.

Descripción: The stress response involves complex physiological mechanisms that maximize behavioral efficacy during attack or defense and is highly conserved in all vertebrates. Key mediators of the stress response are pituitary hormones encoded by the proopiomelanocortin gene (POMC). Despite conservation of physiological function and expression pattern of POMC in all vertebrates, phylogenetic footprinting analyses at the POMC locus across vertebrates failed to detect conserved noncoding sequences with potential regulatory function. To investigate whether ortholog POMC promoters from extremely distant vertebrates are functionally conserved, we used 5′-flanking sequences of the teleost fish Tetraodon nigroviridis POMCα gene to produce transgenic mice. Tetraodon POMCα promoter targeted reporter gene expression exclusively to mouse pituitary cells that normally express Pomc. Importantly, transgenic expression in mouse corticotrophs was increased after adrenalectomy. To understand how conservation of precise gene expression mechanisms coexists with great sequence divergence, we investigated whether very short elements are still conserved in all vertebrate POMC promoters. Multiple local sequence alignments that consider phylogenetic relationships of ortholog regions identified a unique 10-bp motif GTGCTAA(T/G)CC that is usually present in two copies in POMC 5′-flanking sequences of all vertebrates. Underlined nucleotides represent totally conserved sequences. Deletion of these paired motifs from Tetraodon POMCα promoter markedly reduced its transcriptional activity in a mouse corticotropic cell line and in pituitary POMC cells of transgenic mice. In mammals, the conserved motifs correspond to reported binding sites for pituitary-specific nuclear proteins that participate in POMC transcriptional regulation. Together, these results demonstrate that mechanisms that participate in pituitary-specific and hormonally regulated expression of POMC have been preserved since mammals and teleosts diverged from a common ancestor 450 million years ago despite great promoter sequence divergence. Copyright © 2007 by The Endocrine Society.

Descripción: Background: Alzheimer's disease (AD) is characterized by a neurodegenerative progression that alters cognition. On a phenotypical level, cognition is evaluated by means of the MiniMental State Examination (MMSE) and the post-morten examination of Neurofibrillary Tangle count (NFT) helps to confirm an AD diagnostic. The MMSE evaluates different aspects of cognition including orientation, short-term memory (retention and recall), attention and language. As there is a normal cognitive decline with aging, and death is the final state on which NFT can be counted, the identification of brain gene expression biomarkers from these phenotypical measures has been elusive. Methodology/Principal Findings: We have reanalysed a microarray dataset contributed in 2004 by Blalock et al. of 31 samples corresponding to hippocampus gene expression from 22 AD subjects of varying degree of severity and 9 controls. Instead of only relying on correlations of gene expression with the associated MMSE and NFT measures, and by using modern bioinformatics methods based on information theory and combinatorial optimization, we uncovered a 1,372-probe gene expression signature that presents a high-consensus with established markers of progression in AD. The signature reveals alterations in calcium, insulin, phosphatidylinositol and wnt-signalling. Among the most correlated gene probes with AD severity we found those linked to synaptic function, neurofilament bundle assembly and neuronal plasticity. Conclusions/Significance: A transcription factors analysis of 1,372-probe signature reveals significant associations with the EGR/KROX family of proteins, MAZ, and E2F1. The gene homologous of EGR1, zif268, Egr-1 or Zenk, together with other members of the EGR family, are consolidating a key role in the neuronal plasticity in the brain. These results indicate a degree of commonality between putative genes involved in AD and prion-induced neurodegenerative processes that warrants further investigation. © 2010 Go ́mez Ravetti et al.

Descripción: Using quantitative real-time PCR, the expression of mRNAs encoding three transport-related proteins and one putative housekeeping protein was analyzed in anterior and posterior gills of the euryhaline crab Chasmagnathus granulatus following transfer from isosmotic conditions (30‰ salinity) to either dilute (2‰) or concentrated (45‰) seawater. Modest changes were observed in the abundance of mRNAs encoding the housekeeping protein arginine kinase and the vacuolar-type H+-ATPase B-subunit, both of which were highly expressed under all conditions. By contrast, the expression of Na +/K+-ATPase α-subunit mRNA and Na+/K +/2Cl- cotransporter mRNA was strongly responsive to external salinity. During acclimation to dilute seawater, cotransporter mRNA increased 10-20-fold in posterior gills within the first 24 h while Na +/K+-ATPase α-subunit mRNA increased 35-55-fold. During acclimation to concentrated seawater, cotransporter mRNA increased 60-fold by 96 h and Na+/K+-ATPase α-subunit increased approximately 25-fold in posterior gills. Our results indicate a complex pattern of transcriptional regulation dependent upon the direction of salinity change and the developmental background of the gills.

Descripción: The transcription factor TCERG1 (also known as CA150) associates with RNA polymerase II holoenzyme and alters the elongation efficiency of reporter transcripts. TCERG1 is also found as a component of highly purified spliceosomes and has been implicated in splicing. To elucidate the function of TCERG1, we used short interfering RNA-mediated knockdown followed by en masse gene expression analysis to identify its cellular targets. Analysis of data from HEK293 and HeLa cells identified high confidence targets of TCERG1. We found that targets of TCERG1 were enriched in microRNA-binding sites, suggesting the possibility of post-transcriptional regulation. Consistently, reverse transcription-PCR analysis revealed that many of the changes observed upon TCERG1 knockdown were because of differences in alternative mRNA processing of the 3′-untranslated regions. Furthermore, a novel computational approach, which can identify alternatively processed events from conventional microarray data, showed that TCERG1 led to widespread alterations in mRNA processing. These findings provide the strongest support to date for a role of TCERG1 in mRNA processing and are consistent with proposals that TCERG1 couples transcription and processing. © 2008 by The American Society for Biochemistry and Molecular Biology, Inc.

Descripción: VjbR is a LuxR homolog that regulates transcription of many genes including important virulence determinants of the facultative intracellular pathogen Brucella abortus. This transcription factor belongs to a family of regulators that participate in a cell-cell communication process called quorum sensing, which enables bacteria to respond to changes in cell population density by monitoring concentration of self produced autoinducer molecules. Unlike almost all other LuxR-type proteins, VjbR binds to DNA and activates transcription in the absence of any autoinducer signal. To investigate the mechanisms by which Brucella induces VjbR-mediated transcriptional activation, and to determine how inappropriate spatio-temporal expression of the VjbR target genes is prevented, we focused on the study of expression of vjbR itself. By assaying different parameters related to the intracellular lifestyle of Brucella, we identified a restricted set of conditions that triggers VjbR protein expression. Such conditions required the convergence of two signals of different nature: a specific pH value of 5.5 and the presence of urocanic acid, a metabolite involved in the connection between virulence and metabolism of Brucella. In addition, we also observed an urocanic acid, pH-dependent expression of RibH2 and VirB7, two additional intracellular survival-related proteins of Brucella. Analysis of promoter activities and determination of mRNA levels demonstrated that the urocanic acid-dependent mechanisms that induced expression of VjbR, RibH2, and VirB7 act at the post-transcriptional level. Taken together, our findings support a model whereby Brucella induces VjbR-mediated transcription by modulating expression of VjbR in response to specific signals related to the changing environment encountered within the host. © 2012 Arocena et al.

Descripción: The Saccharomyces cerevisiae UGA4 gene encodes a permease capable of importing γ-aminobutyric acid (GABA) and δ-aminolevulinic acid (ALA) into the cell. GABA-dependent induction of this permease requires at least two positive-acting proteins, the specific factor Uga3 and the pleiotropic factor Uga35/Dal81. UGA4 is subjected to a very complex regulation, and its induction is affected by the presence of extracellular amino acids; this effect is mediated by the plasma membrane amino acid sensor SPS. Our results show that leucine affects UGA4 induction and that the SPS sensor and the downstream effectors Stp1 and Stp2 participate in this regulation. Moreover, we found that the Uga3 and Uga35/Dal81 transcription factors bind to the UGA4 promoter in a GABA-dependent manner and that this binding is impaired by the presence of leucine. We also found that the Leu3 transcription factor negatively regulates UGA4 transcription, although this seems to be through an indirect mechanism. © 2010, American Society for Microbiology.