PRI1 is an essential gene (1); it encodes the smallest subunit of DNA polymerase alpha (6), formerly called DNA polymerase I (7); reviewed in 3, 8; also see 6). 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 invloved 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. Purified Pri1p is sufficient to synthesize RNA primers on a DNA template, although primer extension in more efficient in the presence of Pri2p 2. 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).

DNA primase may also couple DNA replication to the DNA damage checkpoint. A mutation in MEC3, which encodes a DNA damage checkpoint protein, can suppress the cold sensitivity of the pri1-2 mutant (12). Another mutation in PRI1, pri1-M4, causes sensitivity to DNA damaging agents and a defect in the G1-S phase DNA damage response (13).

Conditional mutations in PRI1 show altered DNA synthesis at the restrictive temperature (14), as well as increased mitotic intrachromosomal recombination and spontaneous mutation rates (15).

Like many other genes encoding DNA replication proteins, PRI1 is transcribed during late G1 and S phases of the cell cycle (16); however, all four subunits of polymerase alpha are present in a complex throughout the cell cycle (17).FU,PI, Though the mouse Pri1p homolog is very similar to the yeast protein, it cannot complement a pri1 mutation (18).

Last updated: 1999-05-07