Question

We know that Beta clamp in bacteria has two subunits and takes the shape of a ring. Which of this will be characteristic of PCNA which is a beta clamp homologue for eukaryotes?

(a) Two subunits forming ring

(b) Three subunits forming ring

(c) Four subunits forming figure 8 like structure

(d) Four subunits forming a larger ring

I had been asked this question in final exam.

Query is from DNA Replication Eukaryotes in chapter DNA Replication of Cytogenetics

Answer 1

Correct answer is (b) Three subunits forming ring

Best explanation: PCNA has three subunits but its structure is similar (ring) like two subunit beta clamp. Larger ring formation would be unreasonable as the basic structure of DNA is exactly the same for both prokaryotes and eukaryotes.