We are glad to announce that Ramakrishna Mission Vivekananda Educational and Research Institute (RKMVERI) will be conducting a special colloquium on “Fundamental mechanism of transcription in bacteria” on 15 May 2026, 12 Noon at Seminar Hall, Narendrapur Campus.

Speaker :  Prof. Jayanta Mukhopadhyay, Bose Institute
Co-ordinator: Prof. Abhijit Chakrabarti

Abstract

In this talk, I will cover two aspects of transcription: RNAP assembly in B. subtilis and ‘s cyle’ in B. subtilis and M. tuberculosis.

RNAP assembly: The bacterial RNA polymerase (RNAP) core enzyme, responsible for transcription, is composed of five conserved subunits: α₂, β, β′, and ω. In Escherichia coli, RNAP assembly follows a well-established sequential pathway: α + α → α₂ → α₂β → α₂ββ′(ω). This canonical scheme has long been considered universal. Here we show that in Bacillus subtilis, RNAP assembly proceeds not only via the canonical route but also through an alternative pathway: α + α → α₂ → α₂β′(ω) → α₂ββ′(ω). We provide in vivo evidence for both α₂β and α₂β′ intermediates in B. subtilis, whereas E. coli supports only the α₂β intermediate. These findings uncover a previously unrecognized plasticity in bacterial RNAP assembly, attributable to distinct α–β and α–β′ interfaces in different lineages. Our results highlight the evolutionary diversification of RNAP assembly and suggest new opportunities for developing species-specific antibiotics that target lineage-dependent assembly pathways.

σ cycle: A “σ cycle” in which the initiation factor σ associates with RNA polymerase (RNAP) core enzyme to permit transcription initiation and dissociates from RNAP core enzyme to permit transcription elongation, has been proposed to occur and to be an essential step for σ-exchange, with all principal σ factors from all bacteria. These proposals were based on studies of the principal σ factor of Escherichia coli, σ70, which, generally, albeit not obligatorily, is released from RNAP upon the transition from transcription initiation to elongation. Here, we show that, in contrast to E. coli σ70, the Bacillus subtilis principal σ factor, σA, is not released and is retained on the RNAP core throughout transcription elongation. We further show that a mutant E. coli σ70 derivative lacking σ region 1.1 (σ R1.1) is not released and is retained on RNAP core throughout transcription elongation. We also observe that B. subtilis σA and the mutant E. coli σ70 derivative lacking σ R1.1 interact much more stably with RNAP than full-length E. coli σ70.  We further observed that in M. tuberculosis, the principal σ factor σA and the alternative σ factor σE are immediately or stochastically released upon the transition from transcription initiation to elongation, whereas the other sigma factor, σF, is retained throughout the elongation. Incidentally, σF contains all three σ regions except region 1.1.  Our results indicate that the σ cycle is not a universal phenomenon in bacteria; the σ factor that includes all three σ regions except 1.1 is likely to be retained in the elongation complex. 

Please join the penultimate Friday colloquium of the present semester.