Kinetics of dCTP incorporation opposite to 7,8-dihydro-8-oxoguanine with different 5' nearest neighbors by yeast polymerase eta.

Translesion synthesis (TLS), an important mechanism in cells refers to bypassing the DNA damage blockage on replication fork. Yeast TLS polymerase eta (poleta) is able to bypass 7,8-dihydro-8-oxoguanine (8-oxoG) on DNA with high fidelity by incorporation of dCTP opposite 8-oxoG rather than dATP to avoid G to T transversion mutation. We have shown the 5' nearest base next to 8-oxoG affects the G to T mutation by yeast and human poleta previously. In this study, the insertion efficiency of dCTP opposite 8-oxoG in various DNA sequences was kinetically investigated using yeast poleta. Based on K(m) and V(max), we demonstrated that the insertion efficiencies were also influenced by the 5' neighboring nucleotide next to 8-oxoG. The lowest V(max)/K(m) was observed when cytosine was 5' neighbouring base to 8-oxoG, in agreement with previous results in which dCTP incorporation to 8-oxoG was lowest when cytosine is on the 5'-side next to the lesion.

Influence of neighbouring base sequences on the mutagenesis induced by 7,8-dihydro-8-oxoguanine in yeast.

We have analysed the influence of neighbouring base sequences on the mutagenesis induced by 7,8-dihydro-8-oxoguanine (8-oxoG or G(o)), a typical oxidative lesion of DNA, using the yeast oligonucleotide transformation technique. Two oligonucleotides, oligo-CCG(o) and oligo-CGG(o), each possessing a single 8-oxoG residue and represented by the sequences 5'-CCG(o)-3' and 5'-CGG(o)-3', respectively, were introduced into a chromosome of Saccharomyces cerevisiae and their mutagenic potentials were compared. In a wild-type strain, 8-oxoG showed very weak mutagenic potential in both cases. However, the lesion in 5'-CCG(o)-3' can cause efficient G-to-T transversion in a strain lacking the rad30 gene which encodes yeast DNA polymerase eta (Ypoleta). To explore the properties associated with this translesion synthesis (TLS), the same two oligonucleotides possessing an 8-oxoG were used as templates for a standing-start primer extension assay, and the nucleotide incorporation opposite 8-oxoG was investigated. We found that dATP incorporation opposite 8-oxoG with Ypoleta was low for both sequences. In particular, very low dATP incorporation was observed for the 5'-CCG(o)-3' sequence. These results account for the efficient inhibition of mutagenesis by Ypoleta. TLS plays an important role in one DNA sequence in terms of avoiding mutagenesis induced by 8-oxoG in yeast. In contrast, human yeast DNA polymerase eta showed higher dATP incorporation rates even with the 5'-CCG(o)-3' sequence.