The C-terminus of Dpb2 is required for interaction with Pol2 and for cell viability

DNA polymerase epsilon (Pole epsilon) participates in the synthesis of the leading strand during DNA replication in Saccharomyces cerevisiae. Pol epsilon comprises four subunits: the catalytic subunit, Pol2, and three accessory subunits, Dpb2, Dpb3 and Dpb4. DPB2 is an essential gene with unclear function. A genetic screen was performed in S. cerevisiae to isolate lethal mutations in DPB2. The dpb2-200 allele carried two mutations within the last 13 codons of the open reading frame, one of which resulted in a six amino acid truncation. This truncated Dpb2 subunit was co-expressed with Pol2, Dpb3 and Dpb4 in S. cerevisiae, but this Dpb2 variant did not co-purify with the other Pol epsilon subunits. This resulted in the purification of a Pol2/Dpb3/Dpb4 complex that possessed high specific activity and high processivity and holoenzyme assays with PCNA, RFC and RPA on a single-primed circular template did not reveal any defects in replication efficiency. In conclusion, the lack of Dpb2 did not appear to have a negative effect on Pol epsilon activity. Thus, the C-terminal motif of Dpb2 that we have identified may instead be required for Dpb2 to fulfill an essential structural role at the replication origin or at the replication fork.