Identification of gene products required for in vitro formation of the internal peptides of bacteriophage T4

Abstract

In vitro formation of both bacteriophage T4 internal peptides (II and VII) from preexisting precursor protein was shown to require the product of T4 gene 21. The proteolytic factor was detectable in extracts of cells infected with certain phage mutants blocked in early steps of head assembly but could not be demonstrated in extracts of T4 wild-type infected cells. This finding suggests that the proteolytic factor is inactivated during normal phage assembly. The product of T4 gene 22 appears to be the precursor of peptide VII but not of peptide II.

Head morphogenesis of complex double-stranded deoxyribonucleic acid bacteriophages.

“…Whether the 21-coded proteinase is the only enzyme in T4 processing, however, is not known. Attention has been drawn to the fact that although this proteinase specifically cleaves certain glutamic acid-alanine linkages (160, 335), the amino-terminal residues of peptides II and VII are glycine and lysine, respectively (84,119).…”

Proteolytic cleavage and structural transformation: Their relationship in bacteriophage T4 capsid maturation

“…purified esps shows no indication of an unaccounted candidate polypeptide. Multiple cleavage events might possibly generate smaller polypeptides undetected by our gels which could remain associated with the particle.However, we feel this to be unlikely, since examination of phage and cell extracts [36,37] have afforded no evidence of any such gp23-derived peptide.…”

Precursors of the T4 internal peptides

“…The precursor of internal peptide VII is p22. As described previously (6), the in vitro formation of both internal peptides II and VII can be effected when the total unfractionated protein from cells infected with a phage mutant blocked in cleavage is the substrate. Fractionated substrate protein, highly enriched for p22, was found, however, to yield peptide VII but not peptide II.…”

“…Samples of 14C-labeled proteins eluted from acrylamide gels were subjected to proteolytic cleavage with an extract of e -23--infected cells in 0.1 M Tris-hydrochloride, pH 7.8, as the source of cleaving activity. The extract was prepared as described previously (6,7) and was concentrated to between 30 and 40 mg of protein per ml, as estimated by the Folin-Ciocalteau reaction with bovine serum albumin as a standard. The final concentration of extract protein in the incubation mixture was 20 mg/ml.…”

“…That the principal core protein p22 is extensively degraded suggests the possibility that the internal peptides are fragments of p22. In a previous report (6), indirect evidence was presented in support of this precursor-product relationship in the case of peptide VII. The same studies indicated, however, that p22 is not the precursor of peptide II.…”