Initiation of Escherichia coli chromosomal replication is a key event in the bacterial growth cycle. The long term objectives of this proposed research are to obtain a biochemical understanding of the initiation of DNA replication and its coordination to cell growth. dnaA protein plays a central role in the initiation process and appears to determine the time in the bacterial cell cycle when initiation of replication occurs. This protein also appears to synchronize this process at multiple replication origins in a rapidly growing cell, and regulates the expression of its own gene and of several other genes of e. coli. One approach to further understanding of the role of dnaA protein in E coli is by the production and analysis of mutant forms of dnaA protein in comparison with its wild type counterpart. The second involves the interaction of mutant forms of dnaA protein with dnaK, grpE, and dnaJ heat shock proteins which appear to influence replication activity and may represent a mechanism for regulation of the initiation process. The third approach involves correlation of structural domains of dnaA protein to its various activities by use of monoclonal antibodies and by site-specific mutagenesis. While this research addresses a basic biochemical problem such findings may be useful in understanding the mechanism of chromosomal replication and its regulation in higher organisms. These findings may be useful in the design of agents which promote or interfere with cell growth in plants and animals.