Functions and properties related to the tail fibers of bacteriophage T4

Abstract

It is shown that adsorbability of T4 is regularly correlated with the extended state of the tail fibers, suggesting that in T4 fiber extension is a necessary condition for adsorption. Furthermore the extension and retraction of fibers is correlated with the dual sedimentation of T4 observed during ultracentrifugation. For T4, 38, which requires tryptophan for adsorption, electron microscopy shows the tail fibers to be extended in the presence of tryptophan and retracted in its absence. Phages with retracted fibers (no tryptophan) show a faster sedimentation than those with extended fibers (with tryptophan). In the absence of tryptophan T4, 38 does not show fiber extension even at pH 7, a condition sufficient for nontryptophan-requiring T4, whose fibers are retracted at pH 5. A conditional lethal mutation in gene 37 of phage T4D results in phages which lack tail fibers entirely. These phages no longer adsorb. In the ultracentrifuge, only the fast form can be observed whether at pH 7 or 5. Phages with extended fibers are more rapidly inactivated by ultrasonic waves than phages with retracted fibers. Measurements on electron micrographs show that the head size of T4 is invariant. A model of the functioning fiber apparatus is proposed and discussed.