PMID: 30755604
Lin W, Mandal S, Degen D, Cho MS, Feng Y, Das K, Ebright RH
Structural basis of ECF-sigma-factor-dependent transcription initiation.
Nat Commun. 2019 Feb 12;10(1):710. doi: 10.1038/s41467-019-08443-3.
Extracytoplasmic (ECF) sigma factors, the largest class of alternative sigma factors, are related to primary sigma factors, but have simpler structures, comprising only two of six conserved functional modules in primary sigma factors: region 2 (sigmaR2) and region 4 (sigmaR4). Here, we report crystal structures of transcription initiation complexes containing Mycobacterium tuberculosis RNA polymerase (RNAP), M. tuberculosis ECF sigma factor sigma(L), and promoter DNA. The structures show that sigmaR2 and sigmaR4 of the ECF sigma factor occupy the same sites on RNAP as in primary sigma factors, show that the connector between sigmaR2 and sigmaR4 of the ECF sigma factor-although shorter and unrelated in sequence-follows the same path through RNAP as in primary sigma factors, and show that the ECF sigma factor uses the same strategy to bind and unwind promoter DNA as primary sigma factors. The results define protein-protein and protein-DNA interactions involved in ECF-sigma-factor-dependent transcription initiation.