Fidelity and damage bypass ability of Schizosaccharomyces pombe Eso1 protein, comprised of DNA polymerase η and sister chromatid cohesion protein Ctf7

DNA polymerase eta (Pol eta) functions in error-free bypass of ultraviolet light-induced DNA lesions, and mutational inactivation of Pol eta in humans causes the cancer prone syndrome, the variant form of xeroderma pigmentosum (XPV). Both Saccharomyces cerevisiae and human Pol eta efficiently insert two adenines opposite the two thymines of a cyclobutane pyrimidine dimer. Interestingly, in the fission yeast Schizosaccharomyces pombe, the eso1(+) encoded protein is comprised of two domains, wherein the NH2 terminus is highly homologous to Pol eta, and the COOH terminus is highly homologous to the S. cerevisiae Ctf`7 protein which is essential for the establishment of sister chromatid cohesion during S phase. Here we characterize the DNA polymerase activity of S. pombe GST-Eso1 fusion protein and a truncated version containing only the Pol eta domain. Both proteins exhibit a similar DNA polymerase activity with a low processivity, and steady-state kinetic analyses show that on undamaged DNA, both proteins misincorporate nucleotides with frequencies of similar to 10(-2) to 10(-3). We also examine the two proteins for their ability to replicate a cyclobutane pyrimidine dimer-containing DNA template and find that both proteins replicate through the lesion equally well. Thus, fusion with Ctf`7 has no significant effect on the DNA replication or damage bypass properties of Pol eta. The possible role of Ctf`7 fusion with Pol eta in the replication of Cohesin-bound DNA sequences is discussed.