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Publication Abstract from PubMed

Initiation of transcription requires the formation of the "open" promoter complex (RPo). For this, the sigma subunit of bacterial RNA polymerase (RNAP) binds to the nontemplate strand of the -10 element sequence of promoters and nucleates DNA unwinding. This is accompanied by a cascade of conformational changes on RNAP, the exact mechanics of which remains elusive. Here, using single-molecule Forster resonance energy transfer and cryo-electron microscopy, we explored the conformational landscape of RNAP from the human pathogen Mycobacterium tuberculosis upon binding to a single-stranded DNA (ssDNA) fragment that includes the -10 element sequence (-10 ssDNA). We found that like the transcription activator RNAP-binding protein A, -10 ssDNA induced sigma subunit loading onto the DNA/RNA channels of RNAP. This triggered RNAP clamp closure and unswiveling that are required for RPo formation and RNA synthesis initiation. Our results reveal a mechanism of ssDNA-guided RNAP maturation and identify the sigma subunit as a regulator of RNAP conformational dynamics.

Single-stranded DNA drives sigma subunit loading onto mycobacterial RNA polymerase to unlock initiation-competent conformations.,Vishwakarma RK, Marechal N, Morichaud Z, Blaise M, Margeat E, Brodolin K Nucleic Acids Res. 2025 Apr 10;53(7):gkaf272. doi: 10.1093/nar/gkaf272. PMID:40240004^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.