The Functional and Regulatory Roles of Sigma Factors in Transcription

In prokaryotic cells, a single subunit of RNA polymerase, called sigma, orchestrates the process of transcription initiation. Sigma binds to the multisubunit coreRNA polymerase (α2ββ′), creating RNA polymeraseholoenzyme (α2ββ′σ), which performs transcription initiation. Holoenzyme recognizes the two conserved hexamer sequences that constitute a prokaryotic promoter,exposes the single-stranded DNA template necessary fortranscription initiation, and begins synthesizing thenascent RNA chain. When the nascent RNA is five to tennucleotides long, sigma is released, terminating the initiation phase of transcription. Core RNA polymerase thencarries out the elongation and termination phases of transcriptio...