Bacteriophage phi 29 proteins required for in vitro DNA-gp3 packaging

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Abstract
In vitro assembly of bacteriophage .vphi.29 in crude extracts involves efficient packaging of a DNA-protein complex (DNA-gp3) into a prohead with the aid of the gene 16 product (gp16) and subsequent assembly of neck and tail proteins. To define the viral proteins required for the DNA-gp3 encapsidation phase, biologically active proheads and DNA-gp3 were purified and a chimeric plasmid, pUM101, which contained and expressed gene 16 of .vphi.29 and no other viral genes, was constructed. The plasmid-specified gp16 was both necessary and sufficient to package 24% of the DNA-gp3 added to the purified proheads and the DNA-filled heads so produced were efficiently complemented to infectious phage by the addition of neck and tail proteins. Purified proheads and DNA-gp3 gave linear dose-response curves with slopes of .apprx. 1: a 4-fold dilution of gp16 resulted in a 1000-fold reduction of .vphi.29, suggesting a requirement for multiple copies of this protein.