Role of yeast Rad5 and its human orthologs, HLTF and SHPRH in DNA damage tolerance

In the yeast Saccharomyces cerevisiae, the Rad6–Rad18 DNA damage tolerance pathway constitutes a major defense system against replication fork blocking DNA lesions. The Rad6–Rad18 ubiquitin-conjugating/ligase complex governs error-free and error-prone translesion synthesis by specialized DNA polymerases, as well as an error-free Rad5-dependent postreplicative repair pathway. For facilitating replication through DNA lesions, translesion synthesis polymerases copy directly from the damaged template, while the Rad5-dependent damage tolerance pathway obtains information from the newly synthesized strand of the undamaged sister duplex. Although genetic data demonstrate the importance of the Rad5-dependent pathway in tolerating DNA damages, there has been little understanding of its mechanism. Also, the conservation of the yeast Rad5-dependent pathway in higher order eukaryotic cells remained uncertain for a long time. Here we summarize findings published in recent years regarding the role of Rad5 in promoting error-free replication of damaged DNA, and we also discuss results obtained with its human orthologs, HLTF and SHPRH.