The Pol ? variant containing exon ? is deficient in DNA polymerase but has full dRP lyase activity.

ABSTRACT: DNA polymerase (Pol) ? is a key enzyme in base excision repair (BER), an important repair system for maintaining genomic integrity. We previously reported the presence of a Pol ? transcript containing exon ? (105-nucleotide) in normal and colon cancer cell lines. The transcript carried an insertion between exons VI and VII and was predicted to encode a ~42?kDa variant of the wild-type 39?kDa enzyme. However, little is known about the biochemical properties of the exon ?-containing Pol ? (exon ? Pol ?) variant. Here, we first obtained evidence indicating expression of the 42?kDa exon ? Pol ? variant in mouse embryonic fibroblasts. The exon ? Pol ? variant was then overexpressed in E. coli, purified, and characterized for its biochemical properties. Kinetic studies of exon ? Pol ? revealed that it is deficient in DNA binding to gapped DNA, has strongly reduced polymerase activity and higher Km for dNTP during gap-filling. On the other hand, the 5'-dRP lyase activity of the exon ? Pol ? variant is similar to that of wild-type Pol ?. These results indicate the exon ? Pol ? variant is base excision repair deficient, but does conduct 5'-trimming of a dRP group at the gap margin. Understanding the biological implications of this Pol ? variant warrants further investigation.

SUBMITTER: Dai DP 

PROVIDER: S-EPMC6616571 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature