Two novel human and mouse DNA polymerases of the polX family

We describe here two novel mouse and human DNA polymerases: one (pol lambda ) has homology with DNA polymerase beta while the other one (pol mu) is clo ser to terminal deoxynucleotidyltransferase. However both have DNA polymera se activity In vitro and share similar structural organization, including a BRCT domain, helix-loop-helix DNA-binding motifs and polymerase X domain, mRNA expression of pol lambda is highest in testis and fetal liver, while e xpression of pol mu is more lymphoid, with highest expression both in thymu s and tonsillar B cells. An unusually large number of splice variants is ob served for the pol mu gene, most of which affect the polymerase domain. Exp ression of mRNA of both polymerases is downregulated upon treatment by DNA damaging agents (UV light, gamma-rays or H2O2). This suggests that their bi ological function may differ from DNA translesion synthesis, for which seve ral DNA polymerase activities have been recently described, Possible functi ons are discussed.