On a modification of the gene product P23 according to its use as subunit of either normal capsids of phage T4 or of polyheads

Previous results have shown that the major protein subunits of the capsids of normal T4-heads and of the capsoids of head related variants are identical with, or derived from, gene product P23.In SDS gel electrophoresis, two distinct mobilities are found, suggesting a molecular weight difference of about 20%.The product of gene 23 (P23) is used in the assembly of several morphologically defined head related variants [1][2][3][4].These variants -enumerated in the order of an increased number of other genes obligatorily cooperating in the assembly -are as follows: multilayered polyheads, single-layered polyheads, isometric z-particles, prolate r-particles, isometric heads, prolate heads [3].By different methods, evidence was provided that the major component of all these particles is identical with, or derived from, the same protein produced by gene 23:1) Amber mutants of gene 23 alone or in combination with other appropriately chosen morphopoietic genes are unable to build any of these variants [3,6].2) Dissociation of all the particles into subunits by different reagents (6 M guanidine hydrochloride, 67% acetic acid, pH 13-8 M urea) and subsequent urea gel electrophoresis always shows the same major electrophoretic component M [1, 4, 5] identified as the product ofgene 23 [1,7].3) All these variants have at least one antigenic site in common: tubular capsoids and r-particles share at least one other site, not present on capsids, and, conversely, capsids carry at least one other site not found on tubular forms and r-particles [4,5].As predictable from the results of Sarabhai et al.[8] on the colinearity of protein 23 with its gene, amber mutants in this gene lead to incomplete peptide chains with correspondingly increased electro-~horetic mobility [9, 1].