Functional characterization of Ape1 variants identified in the human population

Apurinic/apyrimidinic (AP) sites are common mutagenic and cytotoxic DNA les ions. Ape1 is the major human repair enzyme for abasic sites and incises th e phosphodiester backbone 5' to the lesion to initiate a cascade of events aimed at removing the AP moiety and maintaining genetic integrity. Through resequencing of genomic DNA from 128 unrelated individuals, and searching p ublished reports and sequence databases, seven amino acid substitution vari ants were identified in the repair domain of human Ape1. Functional charact erization revealed that three of the variants, L104R, E126D and R237A, exhi bited similar to 40-60% reductions in specific incision activity. A fourth variant, D283G, is similar to the previously characterized mutant D283A fou nd to exhibit similar to 10% repair capacity. The most common substitution (D148E; observed at an allele frequency of 0.38) had no impact on endonucle ase and DNA binding activities, nor did a G306A substitution. A G241R varia nt showed slightly enhanced endonuclease activity relative to wild-type. In total, four of seven substitutions in the repair domain of Ape1 imparted r educed function. These reduced function variants may represent low penetran ce human polymorphisms that associate with increased disease susceptibility .