Practice question

Flagellar biosynthesis requires ordered cascade regulated by multiple transcription factors. After early class I master regulator FlhDC activating class II genes encoding hook-basal body, gene fliA encoding sigma28 also known as σ28 or FliA induced. σ28 holoenzyme recognizes promoters of class III late operons encoding filament flagellin, motor proteins, and chemotaxis components after completion basal structure, ensuring proper temporal assembly. FlgM anti-sigma inhibits σ28 until secreted upon hook completion. Mutants lacking σ28 non-motile. By contrast σ70 exponential, σ32 heat shock, σ54 nitrogen regulate unrelated regulons, highlighting σ28 specificity for flagellar expression.