Frag1, a homolog of alternative replication factor C subunits, links replication stress surveillance with apoptosis.

We report the identification and characterization of a potent regulator of genomic integrity, mouse and human FRAG1 gene, a conserved homolog of replication factor C large subunit that is homologous to the alternative replication factor C subunits Elg1, Ctf18/Chl12, and Rad24 of budding yeast. FRAG1 was identified in a search for key caretaker genes involved in the regulation of genomic stability under conditions of replicative stress. In response to stress, Atr participates in the down-regulation of FRAG1 expression, leading to the induction of apoptosis through the release of Rad9 from damaged chromatin during the S phase of the cell cycle, allowing Rad9-Bcl2 association and induction of proapoptotic Bax protein. We propose that the Frag1 signal pathway, by linking replication stress surveillance with apoptosis induction, plays a central role in determining whether DNA damage is compatible with cell survival or whether it requires cell elimination by apoptosis.