POL12 is an essential gene (4); it encodes the second largest (79kD), or B, subunit of DNA polymerase alpha (5), formerly called DNA polymerase I (6; reviewed in 7, 8; also see 5). The B subunit executes its essential function during the initiation of DNA replication (4). Yeast DNA polymerase alpha comprises four subunits, of MW 167 kD (Pol1p), 79 kD (Pol12p), 62 kD (Pri2p), and 48 kD (Pri1p). Polymerase alpha is required for DNA replication; it is involved both in initiation and in priming Okazaki fragments during lagging strand elongation. It has no associated proofreading exonuclease activity; the two smaller subunits form the primase activity that synthesizes short RNA primers in DNA replication. In yeast, DNA polymerase alpha activity is required for premeiotic DNA replication and sporulation and for double-strand break repair (9), but not for other DNA repair synthesis (10, 11). All four subunits of DNA polymerase alpha are assembled, and can be co-immunoprecipitated, throughout the cell cycle (12). In addition, affinity chromatography detects physical interactions between the polymerase and several other proteins (13), including Spt16p and Pob3p 14. The B subunit (Pol12p) is phosphorylated in a cell cycle dependent manner (15); association with the 167 kD subunit (Pol1p) is necessary for B subunit phosphorylation (12). Like many other genes encoding DNA replication proteins, POL12 is transcribed during late G1 and S phases of the cell cycle (15). The POL12 promoter contains two MluI cell cycle boxes (MCBs) (15), which are bound by the Swi6p-Mbp1p complex (reviewed in 16 17).

Last updated: 1999-05-07