Infection of E. coli with bacteriophage T7 results in the formation of a complex between host cell membranes and phage DNA. The structural relationships between the DNA and membranes will be examined by utilizing electron microscopic techniques and by the identification and characterization of specific proteins involved in binding the DNA to membrane. Additional studies will focus on the functional role of host cell membranes in T7 DNA replication and maturation. Evidence has been obtained that the T7 DNA membrane complex contains the enzymatic machinery necessary to support a limited in vitro synthesis of T7 DNA. Experiments will be carried out to isolate and characterize all T7 replication proteins and to determine if DNA-membrane complexes influence their mechanism of action. Attempts will be made to assemble the replication proteins and membrane complex into a structural unit which will promote an extensive synthesis of T7 DNA. In connection with this work we will also examine in detail the enzymology of T7 DNA maturation. By using in vitro complementation analysis T7 proteins will be isolated which have a role in the maturation process. The function of these enzymes in relation to phage morphogenesis will also be studied. Additional studies will be carried out to determine the in vivo function of T7 endonuclease II. Mutants defective in the synthesis of this enzyme will be isolated and the physiological defect occurring after infection with these mutants will be examined. T7 endonuclease II is highly specific in its degradation of T7 DNA. Experiments will be carried out to elucidate the mechanism by which the enzyme exhibits this substrate specificity.