PHAGE T4 HEAD ASSEMBLY AND INITIATION OF INFECTION

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The research focuses on the mechanism of viral DNA packaging and on the construction of phage T4 in vitro packaging-derived cloning vectors. Our work is especially directed toward 1) understanding the structures and functions of the multifunctional phage T4 packaging (prohead and terminase) proteins. The 3- dimensional basis for enzymatic (DNA translocating) and structural (prohead form-determining) roles of the major capsid protein gp23*), of a minor processed enzymatic product (gp23**), and of capsid gene mutants will be determined. The assembly of the DNA entrance (also the prohead initiation) vertex as an integral membrane protein will be examined using overexpression vectors; the role of a catalytic gene product and host systems in the membrane insertion will be determined. Specific packaging mutations in both these prohead proteins will be selected following gene-directed mutagenesis. The DNA terminase proteins which interact with the DNA entrance vertex protein in the prohead have been overexpressed and purified-their mechanisms of action in DNA translocation and concatemer cutting will be investigated. lambda and lambda-pBR322 derivative DNAs can be packaged into T4 heads in vitro. cos and/or P1 DNAs packaged into T4 and recircularized with the homologous site-specific recombination systems should allow development of T4-hybrid megacosmid vectors. We have proposed a novel "spiral-fold" model for packaged phage DNA. Morphological and (with phage ) chemical work can definitively establish this model. Packaged kinked or non-B form DNA will be detected, and its interaction with the DNA binding site in the major capsid protein and its minor processed enzymatic product (gp23**) will be probed. We will determine what DNA structures can be packaged in vivo and in vitro; e.g. whether nicks and heteroduplex loops are excluded from packaged DNA in vitro, and whether the terminase proteins act to discriminate against such structures in coupled DNA repair processes.