Intragenic Complementation among Temperature Sensitive Mutants of Bacteriophage T4d.

gene. in phage, may be defined as the hereditary information determining A the primary structure of a polypeptide chain. In the absence of information concerning mutational alterations of specific proteins, the operational definition of a gene is usually derived from complementation tests. Cells containing two functioning genomes with different recessive mutations in the trans configuration are expected to exhibit a mutant phenotype if the mutations are in the same gene. a wild-type phenotype if the mutations are in different genes. The interpretation of such complementation tests is complicated by the phenomenon of intragenic complementation ( CATCHESIDE and OVERTON 1958). Extensive studies have been made on the complementation properties of mutations in a number of genes in a variety of organisms. In general, it is found that the mutants fall in two classes. “Complementing” mutants complement with at least some other mutants of this class defective in the same gene. “Noncomplementing~’ mutants complement neither with each other nor with the complementing mutants defective in the same gene. The complementation phenotype is generally intermediate between mutant and wild type. The results of the intragenic complementation tests can usually be presented as a complementation map of simple form. Previous studies of complementation properties of conditional lethal mutations of the bacteriophage T4 (EDGAR and LIELAUSIS 1964; EDGAR, DENHARDT and EPSTEIN 1964) showed that amber mutants ( a m ) were of the noncomplementing type while temperature sensitive mutants ( t s ) were of the complementing type. It is the purpose of this paper to show that gene complementation maps of simple form can be derived from the complementation patterns of ts mutants.