Isolation of high-density mutants and identification of nonessential structural proteins in bacteriophage T5: Dispensability of L-shaped tail fibers and a secondary major head protein

Abstract

High-density mutants of bacteriophage T5 were isolated by CsCl isopycnic centrifugation. In all of the mutants isolated, at least one or two phage structural proteins were found to be lost, while no extra inserted or duplicated DNA segments could be found. By morphological examination using an electron microscope and physiological tests, it was shown that one of the proteins lost in the high density mutants corresponded to the structural protein (or one of the structural proteins) of the L-shaped tail fiber and that, in the presence of a straight tail fiber, all L-shaped tail fibers were dispensable to adsorption to bacteria and subsequent DNA injection. A secondary major head protein was also shown to be nonessential.