Response of human DNA polymerase ι to DNA lesions

Lesion bypass is an important mechanism to overcome replication blockage by DNA damage. Translesion synthesis requires a DNA polymerase (Pol), Human Pol iota: encoded by the RAD30B gene is a recently identified DNA polymerase that shares sequence similarity to: Pol eta. To investigate whether human Pol iota plays a role in lesion bypass we examined the response of this polymerase to several types of DNA damage-in vitro. Surprisingly, 8-oxoguanine significantly blocked human Pol iota. Nevertheless, translesion DNA synthesis opposite 8-oxoguanine was observed with increasing concentrations of purified human Pol iota, resulting in predominant C and less frequent A incorporation opposite the lesion. Opposite a template abasic site human Pol iota efficiently incorporated a G, less frequently a T and even less frequently an A. Opposite an AAF-adducted guanine, human Pol iota was able to incorporate predominantly a C, In both cases, however, further DNA synthesis was not observed. Purified human Pol iota responded to a template TT (6-4) photoproduct by inserting predominantly an A opposite the 3' T of the lesion before aborting DNA synthesis. In contrast, human Pol iota was largely: unresponsive to a template TT cis-syn cyclobutane dimer. These results suggest a role for human Pol iota in DNA lesion bypass.