Bacteriophage T4 tail assembly: structural proteins and their genetic identification

We have identified the structural proteins of phage T4 precursor tails. Complete tails, labeled with ¹⁴C-labeled amino acids, were isolated from cells infected with mutants blocked in head assembly. The proteins were characterized by sodium dodecyl sulfate-acrylamide gel electrophoresis and subsequent autoradiography. The complete tails are made up of at least fifteen different species of phage proteins.To identify the genes specifying these proteins we prepared ¹⁴C-labeled amino acid lysates made with amber mutants defective in each of the twenty-one genes involved in tail assembly. Comparison of the gel pattern of the amber mutant lysates with wild type lysates enabled us to identify the following gene products, with molecular weights in parentheses: P6 (85,000); P7 (140,000); P8 (46,000); P9 (34,000); P10 (88,000); P11 (26,000); P12 (55,000); P15 (35,000); P18 (80,000); P19 (21,000); P29 (77,000). These eleven species are all structural proteins of the tail. The genetically unidentified tail proteins have molecular weights of 42,000, 41,000, 40,000 and 35,000. They are likely to be the products of known phage genes which were not resolved in the crowded middle region of the whole lysate gel patterns. The major tail proteins are all synthesized during the late part of the phage growth cycle.The mobilities of the proteins derived from tails did not differ from the mobilities of the proteins when derived from the unassembled pools of subunits accumulating in mutant infected cells, or when derived from complete phage particles.The genes for at least seven of the structural proteins are contiguous on the genetic map. Genes for proteins needed in many copies seem to be clustered separ- ately from genes whose products are needed in only a few copies. Consideration of protein sizes and published mapping data on phage T4 also suggest that the phage structural proteins are, on the average, much larger than the non-structural proteins.The requirement that at least fifteen different species of proteins must come together in forming a phage tail emphasizes the complexity of this morphogenetic process.