The mechanism and control of DNA replication in eukaryotic cells is a fundamental problem in understanding cell proliferation. Studies on both virus and cellular DNA replication origins and the proteins that interact with these sequences will be investigated. A cellular protein, nuclear factor I, binds to the origin of human adenovirus DNA replication and is required for the initiation of DNA synthesis. A detailed study on the cell biology of this protein is proposed, specifically to examine the intracellular localization, protein modification and regulation of activity of nuclear factor I. These studies will also involve clonging the gene encoding nuclear factor I and measuring gene expression throughout the cell cycle. Studies on the binding site of this protein, in both virus and cellular DNAs, are proposed. This work will be extended to include similar studies on a cellular protein that binds to a putative origin of replication in the yeast S. cerevisiae. The function of this protein and its DNA binding site in the replication and maintenance of extrachromosomal plasmids and replication of chromosomal DNA will be investigated. Other DNA sites that bind to this cellular protein will be cloned and it will be determined if they have the capability to replicate autonomously in yeast (ARS activity). The gene encoding this protein will be cloned, leading to genetic analysis of the protein's function in cells.