The proposed research will be concerned with the genetic mechanisms that control DNA replication in T4 phage-infected E. coli. In vivo assay systems are being developed to study the regulation of synthesis and activity of the T4 DNA replication enzymes, and in vitro assays will be used to characterize the participants in the regulatory processes. In studies on the function of the T4 DNA polymerase we will examine the molecular bases for the ability of mutations in the gene for this enzyme to suppress the effects of mutations in the gene for dCMP-hydroxymethylase. It is possible that these two enzymes interact in vivo. These studies will be extended to include possible interactions among other T4 DNA replication proteins. In other work we will (a) attempt the isolation of mutations in cis-acting genetic elements that control phage DNA replication, (b) investigate the possibility that the T4 44-protein is a positive regulator of its own synthesis, and (c) attempt to identify the host function(s) analogous to the T4 gene 41 function (possibly an RNA polymerase). In studies on the regulation of mRNA decay we will further characterize T4 mutants that exhibit increased mRNA stability in infected hosts. Attempts will be made to isolate a phage gene product that controls mRNA stability and to fractionate stable T4-induced mRNA species for analysis of the factors involved in determining their biological stability.