Question

Why does E. coli have several different sigma factors?

A.They allow RNA polymerase I, RNA polymerase II and RNA polymerase III to bind to different promoters.

B.They allow the different subunits of the RNA polymerase holoenzyme to bind to each other.

C.They are redundant in case one is mutated. They all perform the same function.

D.One is needed to transcribe mRNA. A second is needed to transcribe tRNA. And a third is needed to transcribe rRNA.

E.They are used if environmental conditions change and different genes need to be transcribed.

Answer 1

E.They are used if environmental conditions change and different genes need to be transcribed.

In E.coli, multiple sigma factors are present each of which are capable of functioning under different environment and directing the transcription of different genes by the core polymerases. It is a method to control the transcription of different genes in different environments since sigma factors are specific to the promoter sequences in DNA and different sigma factors recongnise different set of promoters thereby regulating the transcription of that specific set of genes.