DNA: REPLICATION REPAIR AND RECOMBINATION
Essential Role of Sna41/Cdc45 in Loading of DNA Polymerase α onto Minichromosome Maintenance Proteins in Fission Yeast*

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Assembly of replication complexes at the replication origins is strictly regulated. Cdc45p is known to be a part of the active replication complexes. In Xenopus egg extracts, Cdc45p was shown to be required for loading of DNA polymerase α onto chromatin. The fission yeast cdc45 homologue was identified as a suppressor for nda4 and named sna41. Nevertheless, it is not known how Cdc45p facilitates loading of DNA polymerase α onto chromatin, particularly to prereplicative complexes. To gain novel insight into the function of this protein in fission yeast, we characterized the fission yeast Cdc45 homologue, Sna41p. We have constructed C-terminally epitope-tagged Sna41p and Polαp and replaced the endogenous genes with the corresponding tagged genes. Analyses of protein-protein interactions in vivo by the use of these tagged strains revealed the following: Sna41p interacts with Polαp throughout the cell cycle, whereas it interacts with Mis5p/Mcm6p in the chromatin fractions at the G1-S boundary through S phase. In an initiation-defective sna41 mutant,sna41 goa1, interaction of Polαp with Mis5p is not observed, although Polαp loading onto the chromatin that occurs before G1 START is not affected. These results show that fission yeast Sna41p facilitates the loading of Polαp onto minichromosome maintenance proteins. Our results are consistent with a model in which loading of Polαp onto replication origins occurs through two steps, namely, loading onto chromatin at preSTART and association with prereplicative complexes at G1-S through Sna41p, which interacts with minichromosome maintenance proteins in a cell cycle-dependent manner.

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Published, JBC Papers in Press, May 8, 2001, DOI 10.1074/jbc.M100007200

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This work was supported in part by grants-in-aid for scientific research on priority areas from the Ministry of Education, Science, Sports and Culture of Japan.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

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Supported by Japan Society for the Promotion of Science Research Fellowships for Young Scientists.