Studies on phage internal proteins. III. Specific binding of T4 internal proteins to T4 DNA

Internal protein precursors (IP) are formed in Escherichia coli B cells, soon after infection with bacteriophage T4. These precursors are cleaved to internal protein products (IP*) in E. coli B infected with a wild type of T4, but not after infection with an amber mutant defective in gene 21. It has been shown that T4 internal protein products (IP*), formed either in vitro or in vivo, interact with T4 DNA, but not with the DNA of E. coli B, Clostridium perfringens, bacteriophage T2, lambda, or ∅X174. The specific binding of T4 internal proteins to T4 DNA is not due to glucose residues on phage DNA, since DNA preparations from a glucosyl transferase mutant (T4 am αgt am βgt) or T4 DNA after digestion with β-glucosidase, retain their ability to bind T4 internal proteins. Internal protein precursors (IP) do not form detectable complexes with phage DNA. The proteins bound to T4 DNA in vitro, have been identified as internal proteins by polyacrylamide gel electrophoresis and have the respective molecular weights of 7600, 8600 and 18,000 d.