Studies on the Additivity of Action of Genes Affecting Host Range in Coliphage

Adsorption and heat inactivation studies were made on a series of host range, turbid (ht) mutants of coliphage T2H to determine the mechanisms of phenotypic expression of these genes and of the additivity of gene effects. The ht mutants adsorb to the resistant cell B/2H at a slower rate than the clear h mutant; double and triple ht mutants adsorb with increased efficiency. Some mutants show increased heat sensitivity compared with the wild type. The kinetics of heat inactivation of the progeny of crosses show discontinuity in rate with time. Phenotypic mixing occurs with respect to both adsorption and heat sensitivity. The evidence supports the conclusion that many ht mutations are in genes controlling the formation of separate protein components and that these proteins are incorporated in different positions in the external phage coat.