Purification of DNA-binding proteins of bacteriophage T3 and their role in in vitro packaging of phage T3 DNA

Abstract

Concatemers of phage DNA are produced in T3 wild-type-infected cells, but no concatemeric DNA is formed in cells infected with amber mutants of T3 gene 3 (3 −-infected cells) or 6 −-infected cells. Three proteins with molecular weights of 32,000, 31,000, and 16,000 are missing in 3 −-infected cells. The cell extract from 3 −-infected cells (3 −-extract) is defective for in vitro packaging of T3 mature DNA. Two proteins which can complement 3 −-extract for in vitro DNA packaging are purified. These proteins are single-stranded DNA-binding proteins (DBPs) with molecular weights of 32,000 and 31,000, which are identical to two of the three proteins missing in 3 −-infected cells. The DBPs have no endonucleolytic activity. 3 −-Extract also lacks endonucleolytic activity. T3 mature DNA is converted to concatemers by the concerted action of the DBPs and the gene 6 product (gp6). The concatemeric DNA is packaged in vitro in the absence of DBPs and gp6. These results indicate that phage T3 DBPs and gp6 play essential roles in the formation of concatemeric DNA during the T3 infection process.