Question

You have created a cell-free (in vitro) transcription system that contains a bacterial gene. It is able to initiate transcription but does so at random locations on the DNA.

Which of the following proteins is most likely missing from the reaction?

A.	Sigma factor
	B.	Rho factor
	C.	RNA polymerase
	D.	5' cap proteins
	E.	DNA polymerase

Answer 1

The protein which is most likely missing, in this case, is the SIGMA FACTOR.

Sigam factor is a type of protein which is when associated with RNA polymerase, the whole complex is known as RNA polymerase holoenzyme. This sigma factor is responsible for the recognition and binding of the RNA polymerase to a specific promoter sequence. After binding, the sigma factor detaches and the RNA polymerase core enzyme begins transcription. Therefore, without the sigma factor, RNA polymerase can't bind to specific sites and will start binding to random locations.

Rho factor is a type of protein involved in the transcription process but it aids in the termination of transcription in prokaryotes. It has no part in the start of transcription or elongation.

RNA polymerase is the enzyme which conducts the transcription process. As the gene is being transcribed, we can say that RNA polymerase is not missing.

5' cap proteins are found in eukaryotic RNA which attaches to it during RNA modification. It protects the eukaryotic RNA from degradation. As the gene mentioned here is from a prokaryotic cell, Cap proteins are not needed here. Further, they are not involved in transcription.

DNA polymerase is the enzyme required for the replication of DNA. Therefore, it has no part here.

HENCE, THE PROTEIN WHICH IS MOST LIKELY MISSING IS SIGMA FACTOR.