CELL CYCLE-DEPENDENT ESTABLISHMENT OF A LATE REPLICATION PROGRAM

DNA replication origins in chromosomes of eukaryotes are activated acc ording to a temporal program. In the yeast Saccharomyces cerevisiae, a ctivation of origins in early S phase appears to be a default state. H owever, cis-acting elements such as telomeres can delay origin activat ion until late S phase, Site-specific recombination was used to separa te origin from telomere in vivo, thereby demonstrating that the signal for late activation is established between mitosis and START in the s ubsequent G(1) phase. Once set, the signal can persist through the nex t S phase in the absence of the telomere, Establishment of the tempora l program and of initiation competence of origins may be coincident ev ents.