Characterization of T-even bacteriophage substructures. II. Tail plates.

Tail plates obtained from T4D amber mutants were examined with respect to sedimentation behavior, subunit molecular weights, amino acid composition, isoelectric points, and morphology. Intact plates had an S(20,w) of 77S from pH 5 to 9. The only conformational change noted was that below pH 5 tail plates readily dimerized yielding vis-à-vis dimers with an S(20,w) of 124S. Dissociated plates consisted of three major proteins with molecular weights of 53 K +/- 5, 31 K +/- 3, and 17 K +/- 2 daltons. The amino acid analyses indicated that plates had a composition distinct from fibers and tubes and were relatively rich in tryptophan. Degradation studies with dimethyl sulfoxide (DMSO) indicated that tail plates had a unique biological structure. After treatment with DMSO, and to some extent without DMSO, or from lysates of defective mutants, tetrad structures were observed in the electron microscope. These structures had an amino acid content and relative amounts of types of subunits similar but not identical to intact plates. It was proposed that plates were composed of nine such tetrads giving rise to a structure with six- and threefold symmetry.