Pol kappa: A DNA polymerase required for sister chromatid cohesion

Establishment of cohesion between sister chromatids is coupled to replicati on fork passage through an unknown mechanism. Here we report that TRF4, an evolutionarily conserved gene necessary for chromosome segregation, encodes a DNA polymerase with beta-polymerase-like properties. A double mutant in the redundant homologs, TRF4 and TRF5, is unable to complete S phase, where as a trf4 single mutant completes a presumably defective S phase that resul ts in a failure of cohesion between the replicated sister chromatids. This suggests that TRFs are a key Link in the coordination between DNA replicati on and sister chromatid cohesion. Trf4 and Trf5 represent the fourth class of essential nuclear DNA polymerases (designated DNA polymerase kappa) in S accharomyces cerevisiae and probably in all eukaryotes.