Question

Which of the Ars operon regulation site is actually preventing RNA polymerase from binding and producing the Ara genes BAD?

(a) O1

(b) O2

(c) P

(d) Z

This question was addressed to me in a national level competition.

My question is from Operons : Lac and Ara topic in chapter Gene Expression : Transcription Prokaryotes of Cytogenetics

Answer 1

Correct choice is (b) O2

For explanation I would say: Although O2 is much farther from the ara promoter P yet it can regulate P as it loops out and reaches the site. On the other hand O1 however being closer doesn’t control the promoter of BAD genes.