The proposed research is designed to study the mechanism of DNA synthesis using bacteriophage T4 infected E. coli as a model system. Emphasis is placed on the studies of (1) phage specified proteins which bind to the host-cell membrane, (2) phage gene products which function in the on-set of DNA replication. One of these proteins, the product of gene 39 will be purified and studied in detail. This unique protein binds to DNA in vitro and is found on the membrane. To characterize the enzymatic function of these proteins, an in vitro DNA replication system will be developed to utilize T4 DNA as template to initiate synthesis. Identifiable fractions that function with DNA, including T4 pre- replicative DNA-binding proteins and membrane fractions containing T4 specified membrane proteins, will be included in the in vitro DNA replication studies.