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. Author manuscript; available in PMC: 2013 Mar 21.
Published in final edited form as: Curr Biol. 2001 Nov 27;11(23):R979–R982. doi: 10.1016/s0960-9822(01)00579-6

Figure 1. Replication defects caused by DNA damage in cells mutant for the intra-S phase checkpoint.

Figure 1

Grey circles represent early and black circles late origins. (a) progress of normal chromosome replication (b) replication of chromosomes damaged by MMS. Replication forks much more slowly than normal but are stable and not subject to collapse. Repression of late origin activation depends directly or indirectly on Rad53 and Mec1. (c) replication of MMS-damaged chromosomes in rad53 or mec1 mutants. Replication forks proceed as slowly as in wild-type cells subject to DNA damage. Late origins are activated, and replication forks are unstable, with about 40% stalling irreversibly or collapsing (orange T shapes), so that some DNA regions cannot be replicated. Dotted arrows indicate that the S phase period is extended even more than illustrated here: S phase is complete within 1 hour under normal circumstances, but lasts more than 3 hours in the presence of MMS.