Mcm1 is an essential protein required for the efficient replication of minichromosomes and the transcriptional regulation of early cell cycle genes in Saccharomyces cerevisiae. In this study, we report that Mcm1 is an abundant protein that associates globally with chromatin in a punctate pattern. We show that Mcm1 is localized at replication origins and plays an important role in the initiation of DNA synthesis at a chromosomal replication origin in vivo. Using purified Mcm1 protein, we show that Mcm1 binds cooperatively to multiple sites at autonomously replicating sequences. These results suggest that, in addition to its role as a transcription factor for the expression of replication genes, Mcm1 may influence the local structure of replication origins by direct binding.