DNA polymerases   and   are required for efficient immunoglobulin V gene diversification in chicken

The chicken DT40 B lymphocyte line diversifies its immunoglobulin (Ig) V genes through translesion DNA synthesis-dependent point mutations (Ig hyper-mutation) and homologous recombination (HR)-dependent Ig gene conversion. The error-prone biochemical characteristic of the A family DNA polymerases Pol nu and Pol theta led us to explore the role of these polymerases in Ig gene diversification in DT40 cells. Disruption of both polymerases causes a significant decrease in Ig gene conversion events, although POLN-/-/POLQ(-/-). cells exhibit no prominent defect in HR-mediated DNA repair, as indicated by no increase in sensitivity to camptothecin. Pol eta has also been previously implicated in Ig gene conversion. We show that a POLH-/-/POLN-/-/POLQ(-/-). triple mutant displays no Ig gene conversion and reduced Ig hyper-mutation. Together, these data define a role for Pol nu and Pol theta in recombination and suggest that the DNA synthesis associated with Ig gene conversion is accounted for by three specialized DNA polymerases.