Fidelity and damage bypass ability of Schizosaccharomyces pombe Eso1 protein, comprised of DNA polymerase eta 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 pigmentosu m (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 hi ghly homologous to Pol eta, and the COOH terminus is highly homologous to t he S. cerevisiae Ctf`7 protein which is essential for the establishment of sister chromatid cohesion during S phase. Here we characterize the DNA poly merase activity of S. pombe GST-Eso1 fusion protein and a truncated version containing only the Pol eta domain. Both proteins exhibit a similar DNA po lymerase activity with a low processivity, and steady-state kinetic analyse s show that on undamaged DNA, both proteins misincorporate nucleotides with frequencies of similar to 10(-2) to 10(-3). We also examine the two protei ns for their ability to replicate a cyclobutane pyrimidine dimer-containing DNA template and find that both proteins replicate through the lesion equa lly well. Thus, fusion with Ctf`7 has no significant effect on the DNA repl ication 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 di scussed.