In vitro packaging of bacteriophage T4 DNA

Abstract

Bacteriophage T4 can be formed in an in vitro DNA packaging system which requires addition of exogenous T4 DNA. Extracts prepared from bacteria infected with mutants 20 cs, 17 cs, 16 am, 17 am, or 16 am–17 am contain processed proheads. These appear to be efficient DNA acceptors in the in vitro system. Packaging of mature T4 DNA is more efficient than of concatemeric T4 DNA. The phage yield is proportional to the quantity of DNA and prohead-containing extract added. Activity requires addition of nucleoside triphosphate, Mg 2+, and is inhibited by 9-amino acridine. gpl6 and gp17, the primary T4 DNA packaging gene products, are essential, but 16 am and 17 am mutants appear not to complement each other in vitro. Many T4 recombinants, including multiple recombinants, appear to be generated by in vitro recombination in this system. In vitro T4 DNA packaging conforms to expectations based upon analysis of T4 mutants and head assembly in vivo and displays fundamental similarity to that of other complex double-stranded DNA phages.