Structure and Function of Cdc6/Cdc18Implications for Origin Recognition and Checkpoint Control (original) (raw)

The Cdc6 protein (Cdc18 in fission yeast) is critical for pre-RC assembly. Cdc6/Cdc18 is recruited to replication origins by ORC (Liang et al., 1995; Grallert and Summary Nurse, 1996; Leatherwood et al., 1996). Once localized at replication origins, Cdc6/Cdc18 helps to recruit and Cdc6/Cdc18 is a conserved and essential component load Mcm factors onto DNA in a process that is believed of prereplication complexes. The 2.0 Å crystal structo be ATP dependent (Coleman et al., 1996; Romanowski ture of an archaeal Cdc6 ortholog, in conjunction with et al., 1996; Donovan et al., 1997; Tanaka et al., 1997; a mutational analysis of the homologous Cdc18 pro-Perkins and Diffley, 1998; Weinreich et al., 1999). Deletein from Schizosaccharomyces pombe, reveals novel tion of Cdc6/Cdc18 leads not only to a block in DNA aspects of Cdc6/Cdc18 function. Two domains of replication but also to a loss of checkpoint control, which Cdc6 form an AAA ؉ -type nucleotide binding fold that allows cells to enter mitosis without prior DNA replicais observed bound to Mg•ADP. A third domain adopts tion (Kelly et al., 1993; Piatti et al., 1995). The checkpoint a winged-helix fold similar to known DNA binding modfunction of Cdc6/Cdc18 is mediated by signaling pathules. Sequence comparisons show that the wingedways that block Cdc28/Cdc2 activation at mitosis, and helix domain is conserved in Orc1, and mutagenesis it is dependent on the products of checkpoint control data demonstrate that this region of Cdc6/Cdc18 is genes, such as the hus and rad genes of S. pombe required for function in vivo. Additional mutational (Stewart and Enoch, 1996; Caspari and Carr, 1999). analyses suggest that nucleotide binding and/or hy-Archaea contain orthologs of several eukaryotic replidrolysis by Cdc6/Cdc18 is required not only for procation proteins, including Cdc6/Cdc18 and Mcms (Edgression through S phase, but also for maintenance gell and Doolittle, 1997; Baker and Bell, 1998; Leipe et of checkpoint control during S phase.