Studies on Elongation Stage

Three different DNA polymerases (a, d and e) are involved in supporting DNA replication in all eukaryotes. DNA polymerase a is associated with DNA primase which catalyzes the formation of short oligoribonucleotides on both leading and lagging DNA strands that are elongated for only a short length by DNA polymerase a. On the lagging strand, the Pol a-primase complex acts repetitively and these short chains are elongated further by Pol d. On the leading strand it is now believed that Pol e elongates chains continuously. The action of both Pol d and Pol e require PCNA which is loaded onto DNA by the five subunit complex RFC. PCNA, a circular homotrimeric structure, interacts with Pol d and e and tethers these polymerases to the primer terminus permitting them to act processively during replication. Our laboratory has carried out detailed analyses of the action of the Pol a-primase complex and Pol d. The properties of cloned Pol e a four subunit complex, are now under intensive study. It was recently shown that deletion of the catalytic domain of the large subunit of Pol e in yeasts is not lethal, provided that its C-terminal domain is expressed. The interaction of Pol d with the other known component at the replication fork as well as the precise role of Pol d and Pol e at the replication fork are under investigation.