Question

What is the function of 1^st subunit of sigma factor in σ^70 and σ^43?

(a) It helps to bind sigma to DNA

(b) It helps to bind sigma to core beta subunit

(c) It helps to bind sigma to core alpha subunit

(d) It prevents sigma to bind to DNA

The question was asked during an online interview.

I would like to ask this question from Transcription in Prokaryotes : Sigma Factor topic in chapter Gene Expression : Transcription Prokaryotes of Cytogenetics

Answer 1

Right option is (d) It prevents sigma to bind to DNA

For explanation: The 1^st region forms a flap like structure that blocks the DNA binding sites. This helps to prevent unbound sigma to bind to DNA. That will only block the DNA binding site and lead to no transcription in absence of RNA pol.