Segregation of replicative DNA polymerases during S phase: DNA polymerase ?, but not DNA polymerases ?/?, are associated with lamins throughout S phase in human cells.

ABSTRACT: DNA polymerases (Pol) ?, ?, and ? replicate the bulk of chromosomal DNA in eukaryotic cells, Pol ? being the main leading strand and Pol ? the lagging strand DNA polymerase. By applying chromatin immunoprecipitation (ChIP) and quantitative PCR we found that at G(1)/S arrest, all three DNA polymerases were enriched with DNA containing the early firing lamin B2 origin of replication and, 2 h after release from the block, with DNA containing the origin at the upstream promoter region of the MCM4 gene. Pol ?, ?, and ? were released from these origins upon firing. All three DNA polymerases, Mcm3 and Cdc45, but not Orc2, still formed complexes in late S phase. Reciprocal ChIP of the three DNA polymerases revealed that at G(1)/S arrest and early in S phase, Pol ?, ?, and ? were associated with the same nucleoprotein complexes, whereas in late S phase Pol ? and Pol ?/? were largely associated with distinct complexes. At G(1)/S arrest, the replicative DNA polymerases were associated with lamins, but in late S phase only Pol ?, not Pol ?/?, remained associated with lamins. Consistently, Pol ?, but not Pol ?, was found in nuclear matrix fraction throughout the cell cycle. Therefore, Pol ? and Pol ?/? seem to pursue their functions at least in part independently in late S phase, either by physical uncoupling of lagging strand maturation from the fork progression, or by recruitment of Pol ?, but not Pol ?, to post-replicative processes such as translesion synthesis or post-replicative repair.

SUBMITTER: Vaara M 

PROVIDER: S-EPMC3460436 | biostudies-other | 2012 Sep

REPOSITORIES: biostudies-other