Differential requirement for the N-terminal catalytic domain of the DNA polymerase ε p255 subunit in the mitotic cell cycle and the endocycle

In Drosophila, the 255 kDa catalytic subunit (dpol epsilon p255) and the 58 kDa subunit of DNA polymerase epsilon (dpol epsilon p58) have been identified. The N-terminus of dpol epsilon p255 carries well-conserved six DNA polymerase subdomains and five 3'-> 5' exonuclease motifs as observed with Pole in other species. We here examined roles of dpol epsilon p255 during Drosophila development using transgenic fly lines expressing double stranded RNA (dsRNA). Expression of dpol epsilon p255 dsRNA in eye discs induced a small eye phenotype and inhibited DNA synthesis, indicating a role in the G1-S transition and/or S-phase progression of the mitotic cycle. Similarly, expression of dpol epsilon p255 dsRNA in the salivary glands resulted in small size and endoreplication defects, demonstrating a critical role in endocycle progression. In the eye disc, defects induced by knockdown of dpol epsilon p255 were rescued by overexpression of the C-terminal region of dpol epsilon p255, indicating that the function of this non-catalytic domain is conserved between yeast and Drosophila. However, this was not the case for the salivary gland, suggesting that the catalytic N-terminal region is crucial for endoreplication and its defect cannot be complemented by other DNA polymerases. In addition, several genetic interactants with dpol epsilon p255 including genes related to DNA replication such as RFC, DNA primase, DNA pol eta, Mcm10 and Psf2 and chromatin remodeling such as lswi were also identified. (C) 2012 Elsevier BM. All rights reserved.