Question

You add labeled Uridine analogue to the mixture of DNA and RNA pol in vitro. What are you trying to determine?

(a) Catalytic subunit of RNA pol

(b) Processivity of RNA pol

(c) Presence of DNA – RNA hybrid

(d) Length of DNA already transcribed

I had been asked this question in an interview for job.

This intriguing question originated from Transcription in Prokaryotes : Elongation topic in division Gene Expression : Transcription Prokaryotes of Cytogenetics

Answer 1

Correct choice is (c) Presence of DNA – RNA hybrid

The explanation is: The Uridine analogue can base pair with the RNA pol enzyme when there is a presence of a complementary strand (here DNA). Thus, its incorporation and cross linking will confirm the presence of RNA-DNA hybrid. We use labeled NTP to detect the other processes mentioned.