Initiation of DNA replication acts as a failsafe point in the cell proliferation cycle, because it is a commitment to cell division and, therefore, central to control of the eukaryotic cell cycle (Laskey et al. 1989). In addition, initiation of DNA replication is coupled to programmed changes in gene expression that occur during the life of a single cell as well as during the development of multicellular organisms (Villarreal 1991). Therefore, understanding, at the molecular level, the processes by which DNA replication is initiated is crucial to understanding regulation of cell proliferation, its linkage to gene expression, and its aberrations that lead to diseases such as cancer.