Fig. 6. Bypass of thymine dimers by hPolη motif II single mutants. (A) Mutant hPolη proteins harboring single amino acid substitutions were synthesized in a high-throughput transcription and translation system in the presence of [³⁵S]methionine. Amino acid substitutions in the mutants are indicated along with their position in the protein (e.g. E53A indicates a Glu to Ala substitution at position 53). (B) Bypass of a T–T dimer by the in vitro synthesized mutants was measured in primer extension assays. The position of the lesion (T=T) was four nucleotides downstream from the 3′ primer terminus (arrow), as indicated here and in the template sequence in Figure 1.