Interaction of bacteriophage T4 tail fiber components with a lipopolysaccharide fraction from Escherichia coli

Abstract The inactivation of T4 phage by an Escherichia coli lipopolysaccharide fraction can be blocked by prior incubation of that fraction with phago or certain phage components. Based on this finding, a quantitative LPS ‡ blocking assay analogous to the serum blocking assay of DeMars (1955) has been developed. The LPS blocking assay, electron microscopy and sedimentation have been used to study the interaction of LPS with purified and partially purified phage precursors from mutant-infected cells. All three methods indicate that the tail-fiberless particle and the tail fiber subunit controlled by gene 34 and carrying the A antigen (A half-fiber) do not interact with LPS. By contrast, the whole tail fiber, as well as the half-fiber controlled by genes 35–38 and carrying the B and C antigens (BC′ half-fiber) do interact with LPS, and appear in electron micrographs to become attached to it by their tips. Moreover, the latter half-fiber interacts to the same extent with LPS whether or not it has been acted upon by the products of genes 35 and 36, suggesting that those genes may control attachment to the A half-fiber rather than interaction with LPS. Since the whole fiber is composed of an A half-fiber and a BC′ half-fiber linked end to end, and since the distal tip of the whole fiber is known to make the initial attachment of the phage to the bacterial surface during the adsorption process, it is concluded that the BC′ half-fiber is distal and the A half-fiber proximal to the baseplate in the completed virus particle.