Assembly of bacteriophage T4 tail fibers: identification and characterization of the nonstructural protein gp57

Formation of both the tail fiber and the baseplate of bacteriophage T4 depends on the product of T4 gene 57. A single amber mutation in that gene causes loss of two T4-specific proteins. Their molecular weights are 18,000 and about 6,000, respectively, based on their electrophoretic mobilities in SDS-polyacrylamide gels. E. coli carrying a cloned T4 DNA fragment of about 700 basepairs, which directs the synthesis of the smaller protein only, specifically supports the growth of gene 57 amber mutants. We conclude that the small protein is a functional product of gene 57.