Question

In an experiment you add increasing amount of sigma factor to a mixture of DNA fragment and core polymerase in vitro. You also add [^14C]ATP and  [γ-^32P]ATP in the mixture and check the rate of incorporation. Results show that the incorporation of both of this labels increase on adding more sigma factor. What will you conclude from your observation?

(a) Sigma confers specificity and increases transcription rate

(b) Sigma increases initiation and elongation rate

(c) Sigma increases initiation of transcription rate

(d) Sigma causes faster elongation

This question was addressed to me during an online interview.

The doubt is from Transcription in Prokaryotes : Initiation in section Gene Expression : Transcription Prokaryotes of Cytogenetics

Answer 1

Right answer is (b) Sigma increases initiation and elongation rate

The best explanation: [γ-^32P]ATP incorporation marks more initiation while [^14C]ATP incorporation indicates elongation. As on adding sigma factor both incorporations seems to increase, sigma must increase both initiation and elongation rate.