Identification and characterization of human DNA polymerase beta 2, a DNA polymerase beta -related enzyme

The BRCA1 COOH terminus (BRCT) motif is present in many nuclear proteins that contribute to cell cycle regulation or DNA repair. Polymerase chain reaction-based screening with degenerate primers targeted to the BRCT motif resulted in the isolation of a human cDNA for a previously unidentified DNA Polymerase (designated DNA Polymerase beta2) that is closely related to DNA Polymerase beta (Pol beta). The predicted Pol beta2 protein contains a BRCT motif in its NH(2)-terminal region; its COOH-terminal region exhibits 33% sequence identity to a corresponding region of human Pol beta. The Pol beta2 gene is expressed in a tissue-specific manner, with transcripts being most abundant in testis. A fusion construct comprising Pol beta2 and green Fluorescent protein exhibited a predominantly nuclear localization in transfected HeLa cells. Recombinant human Pol beta2 from insect cells exhibited substantial DNA Polymerase activity, but it did not possess terminal deoxyribonucleotidyl transferase activity. A truncated Pol beta2 mutant lacking the BRCT motif retained substantial DNA Polymerase activity, whereas a mutant Pol beta2 with two alanine point mutations within the DNA Polymerase active site did not. These results indicate that Pol beta2 is a Pol beta-related DNA Polymerase with a BRCT motif that is dispensable for its polymerase activity.