Question

Pol III: (catalytic subunit encoded by polC/dnaE gene):

a) ____; de novo synthesis of new strands of DNA
b) Contains many subunits
c) There are only 10-20/cell
c) Molecular mass of 900 kDa
d) Has no___to ____ ___ activity

Answer 1

In E. coli, the RNA polymerase σ subunit confers specificity to transcription, ensuring that the holoenzyme begins to synthesize mRNA from the correct initiation site.

Step-by-step explanation:

The subject of the question is the role of various subunits of the E. coli RNA polymerase during the transcription process. In E. coli, RNA polymerase is composed of five polypeptide subunits: two α subunits, one β subunit, one β' subunit, and the σ subunit. The four subunits, α, α, β, and β', comprise the polymerase core enzyme, which assembles on the DNA to transcribe mRNA. The β subunit plays a key part by binding to ribonucleoside triphosphates that are incorporated into the mRNA molecule, while the β' subunit binds the DNA template strand.

The fifth subunit, σ, is exclusively involved in transcription initiation and confers transcriptional specificity, ensuring that mRNA synthesis begins at the correct initiation site. Without the σ subunit, the core enzyme would start transcription randomly, leading to nonsensical mRNA sequences. When all subunits, including σ, are present, the complete complex is referred to as the holoenzyme. Therefore, the subunit that confers specificity to transcription is the σ subunit.