Structural insights into σ28-dependent transcription initiation and its regulation by anti-sigma factor in Pseudomonas aeruginosa.

ABSTRACT: Late flagellar genes in Pseudomonas aeruginosa are transcribed by the group 3 sigma factor, FliA (σ28). σ28 drives the expression of flagellin, which assembles into the flagellar filament in this monoflagellated bacterium. This function is suppressed by the anti-sigma factor FlgM. Here, we present the 1.95Å resolution crystal structure of σ28-FlgM complex, along with a 3.4Å structure of σ28RNAP open promoter complex determined using single particle cryo-electron microscopy from P. aeruginosa. The σ28 adopts a compact conformation upon binding to the anti-sigma factor FlgM, which contacts all three domains of the sigma factor. This conformation is neither conducive to interactions with RNA polymerase nor the promoter DNA. The cryo-EM structure reveals base-specific interactions of σ28 domai

SUBMITTER: Sheenu 

PROVIDER: S-EPMC12784957 | biostudies-literature | 2026 Jan

REPOSITORIES: biostudies-literature