The proposed research will be concerned with the genetic mechanisms that control DNA replication in T4 phage-infected E. coli. Defects in the regulation of function (synthesis and activity) of the T4 DNA replication enzymes are being examined to understand this regulation and to gain insights into how viral gene expression is controlled in general. One major aspect of this work deals with elucidation of a mechanism for mRNA decay. A protein is being isolated that plays a role in differential inactivation of mRNA in T4-infected cells. This protein will be used along with purified T4 mRNA species in attempts to reconstruct the mechanism in vitro.