No abstract

Most bacterial RNA polymerases (RNAP) contain five conserved subunits, viz. 2␣, ␤, ␤, and . However, in many Grampositive bacteria, especially in fermicutes, RNAP is associated with an additional factor, called ␦. For over three decades since its identification, it had been thought that ␦ functioned as a subunit of RNAP to enhance the level of transcripts by recycling RNAP. In support of the previous observations, we also find that ␦ is involved in recycling of RNAP by releasing the RNA from the ternary complex. We further show that ␦ binds to RNA and is able to recycle RNAP when the length of the nascent RNA reaches a critical length. However, in this work we decipher a new function of ␦. Performing biochemical and mutational analysis, we show that Bacillus subtilis ␦ binds to DNA immediately upstream of the promoter element at A-rich sequences on the abrB and rrnB1 promoters and facilitates open complex formation. As a result, ␦ facilitates RNAP to initiate transcription in the second scale, compared with minute scale in the absence of ␦. Using transcription assay, we show that ␦-mediated recycling of RNAP cannot be the sole reason for the enhancement of transcript yield. Our observation that ␦ does not bind to RNAP holo enzyme but is required to bind to DNA upstream of the ؊35 promoter element for transcription activation suggests that ␦ functions as a transcriptional regulator.Transcription is the first step in gene regulation in bacteria in which RNA polymerase (RNAP) 3 together with different factors and transcriptional regulators control the gene expression. Bacterial RNAP core enzyme contains five conserved subunits: 2 ␣, ␤, ␤Ј, and . A specificity factor associates with RNAP core enzyme to form RNAP holo enzyme that is able to recognize and initiate transcription at promoters.In certain Gram-positive bacteria, including Bacillus subtilis and Staphylococcus aureus, an additional factor, called ␦, is associated with RNAP. The ␦ factor was first identified in 1975 during the purification of RNAP from phage (SP01)-infected B. subtilis (1). The protein copurified with RNAP, and therefore it was thought that ␦ functions as a subunit of RNAP. Attempts were made to characterize the functional role of the protein in transcription. Several reports suggested that ␦ was involved in promoter selection (2-5) and functioned together with A as an initiation subunit of RNAP (6, 7) or as an allosteric modulator of RNAP conformation in both initiation and the RNAP core recycling phase (5). Other reports showed that ␦ and A bind to RNAP core with negative cooperativity (8, 9), and ␦ has no effect on transcription initiation, the rate of elongation, or termination (5). Using in vitro transcription assays, several groups showed that ␦ enhances the production of transcripts from certain promoters. This increase in transcript yield in the presence of ␦ is attributed to the recycling of RNAP possibly by ␦-mediated release of RNAP from the elongation complex following transcription termination or by inhibiting the formation of s...

We propose a novel mechanism of gene regulation in Mycobacterium tuberculosis where the protein Rv1222 inhibits transcription by anchoring RNA polymerase (RNAP) onto DNA. In contrast to our existing knowledge that transcriptional repressors function either by binding to DNA at specific sequences or by binding to RNAP, we show that Rv1222-mediated transcription inhibition requires simultaneous binding of the protein to both RNAP and DNA. We demonstrate that the positively charged C-terminus tail of Rv1222 is responsible for anchoring RNAP on DNA, hence the protein slows down the movement of RNAP along the DNA during transcription elongation. The interaction between Rv1222 and DNA is electrostatic, thus the protein could inhibit transcription from any gene. As Rv1222 slows down the RNA synthesis, upon expression of the protein in Mycobacterium smegmatis or Escherichia coli, the growth rate of the bacteria is severely impaired. The protein does not possess any significant affinity for DNA polymerase, thus, is unable to inhibit DNA synthesis. The proposed mechanism by which Rv1222 inhibits transcription reveals a new repertoire of prokaryotic gene regulation.

MSMEG_2295 is a TetR family protein encoded by the first gene of a Mycobacterium smegmatis (Msm) operon that expresses the gene for DinB2 (MSMEG_2294), a translesion DNA repair enzyme. We have carried out investigations to understand its function by performing DNA binding studies and gene knockout experiments. We found that the protein binds to a conserved inverted repeat sequence located upstream of the dinB2 operon and several other genes. Using a knockout of MSMEG_2295, we show that MSMEG_2295 controls the expression of at least five genes, the products of which could potentially influence carbohydrate and fatty acid metabolism as well as antibiotic and oxidative stress resistance. We have demonstrated that MSMEG_2295 is a repressor by performing complementation analysis. Knocking out of MSMEG_2295 had a significant impact on pyruvate metabolism. Pyruvate dehydrogenase activity was virtually undetectable in ΔMSMEG_2295, although in the complemented strain, it was high. We also show that knocking out of MSMEG_2295 causes resistance to H2O2, reversed in the complemented strain. We have further found that the mycobacterial growth inhibitor plumbagin, a compound of plant origin, acts as an inducer of MSMEG_2295 regulated genes. We, therefore, establish that MSMEG_2295 functions by exerting its role as a repressor of multiple Msm genes and that by doing so, it plays a vital role in controlling pyruvate metabolism and response to oxidative stress.

Background:The proposed model for promoter escape predicts the destabilization of interactions of region 4 with RNA polymerase and DNA. Results: Using a two-component factor, we show that YvrI, mimicking the region 4, is released, whereas YvrHa, mimicking region 2, is retained after promoter escape. Conclusion: This study validates the proposed mechanism for promoter escape. Significance: This study suggests the possibility of certain -factors to be retained in elongation complex.