Question

Q10. In one to two sentences each, describe the function of each of the
following proteins or protein subunits in DNA replication. In each case, state whether it is found
in bacteria or eukaryotes.

Pol III subunit a

Pol a

b clamp

PCNA

RFC

FEN1

DNA ligase I

SSB

Answer 1

Polymerase III is the principal enzyme which is catalyzed replication in prokaryotes. It is made up of multiple units like α, ε and θ subunits form the core enzyme. a unit has 5'-3' polymerase activity, it added nucleotide to the 3' OH of the replicating strand. (found in bacteria)

Pol a- DNA polymerase alpha has low processivity. It plays an important role during initiation of replication by associating with primase and synthesize short RNA-DNA hybrid (10 nucleotides long RNA followed by 10-20 nucleotide long DNA, found in eukaryotes)

b clamp- found in bacteria, loaded by clamp loader on to DNA to increase the processivity of the DNA polymerase.

PCNA - (Proliferating Cell Nuclear Antigen) It is a sliding clamp found in eukaryotes and increases the processivity of the delta DNA polymerase

RFC - Replication factor C works as a clamp loader complex in eukaryotes. It catalyzes loading of the PCNA (which increases the processivity of the polymerase) on the DNA (present in eukaryotes)

FEN1- Flap endonuclease involved in the replication as well as base excision repair. It is involved in the removal of 5' overhanging flaps on the Okazaki fragments. Its main function in the primary removal process. (present in eukaryotes)

DNA ligase- join the gap between the DNA strands by catalyzing the phosphodiester bond. It connects the Okazaki fragments which are created on the lagging strand of DNA during replication of DNA (found in both bacteria and eukaryotes)

SSB - single-strand binding protein bound with the single-strand DNA which is created by the helicase during replication and prevents its reassociation to form a double strand. ( found in bacteria, in eukaryotes RPA act as SSB)