Replication of the lagging strand: a concert of at least 23 polypeptides.

DNA replication is one of the most important events in living cells, and it is still a key problem how the DNA replication machinery works in its details. A replication fork has to be a very dynamic apparatus since frequent DNA polymerase switches from the initiating DNA polymerase alpha to the processive elongating DNA polymerase delta occur at the leading strand (about 8 x 10(4) fold on both strands in one replication round) as well as at the lagging strand (about 2 x 10(7) fold on both strands in one replication round) in mammalian cells. Lagging strand replication involves a very complex set of interacting proteins that are able to frequently initiate, elongate and process Okazaki fragments of 180 bp. Moreover, key proteins of this important process appear to be controlled by S-phase check-point proteins. It became furthermore clear in the last few years that DNA replication cannot be considered uncoupled from DNA repair, another very important event for any living organism. The reconstitution of nucleotide excision repair and base excision repair in vitro with purified components clearly showed that the DNA synthesis machinery of both of these macromolecular events are similar and do share many components of the lagging strand DNA synthesis machinery. In this minireview we summarize our current knowledge of the components involved in the execution and regulation of DNA replication at the lagging strand of the replication fork.