Fig. 1. Plasmid-encoded wild-type human DNA polymerase η confers UV resistance and catalyzes bypass of cis–syn cyclobutane thymine dimers. (A) hPolη enhances UV resistance of the S.cerevisiae rad30rad52 double mutant that lacks both host Polη (Rad30p) and (Rad52p). Expression of hPolη in rad30rad52 cells increases survival to that observed with rad52 cells. ∗, rad30rad52; O, rad52; Δ, rad30rad52 transformed with pYEX-hPolη. (B) SDS–polyacrylamide gel analysis of the [³⁵S]methionine-labeled products produced by in vitro transcription and translation with either pYEX-hPolη or pYEX-4T (control). Molecular weight markers are shown in the left lane. (C) In vitro bypass of a site-specific cis–syn T–T dimer in a primer extension assay. The template lesion (indicated by T=T) was four nucleotides downstream of the 3′ primer terminus (indicated by an arrow).