Required for replication of the leading DNA strand and for completion of lagging strand synthesis. It is essential for cell cycle progression. a 2'-deoxyribonucleoside 5'-triphosphate + DNA(n) = diphosphate + DNA(n+1) Heterodimer with subunits of 125 kDa and 50 kDa. Interacts with cdc27, however the function of this complex is not known. Belongs to the DNA polymerase delta/II small subunit family.