Particle containing uncleaved major head protein (P23) which is maturable into the head of phage T4

Abstract

PREVIOUS results¹ suggested that τ-particles produced by a phage T4 temperature-sensitive (ts) mutant in gene 24 can be matured into T4 phage heads after a shift to a permissive temperature (temperature shift-down). The experimental evidence which supports this hypothesis can be summarised as follows: (1) the number of τ-particles per bacterium observed after temperature shift-down of a 24⁻ infected culture decreases concomitantly with an increase in the number of normal T4 phage particles; (2) preshift (under nonpermissive conditions) 24⁻ radioactively pulse-labelled cultures produce radioactively labelled normal phage after temperature shift-down; (3) after temperature shift-down, preshift radioactively labelled major head protein P23 (molecular weight 59,000) is cleaved into P23^* (molecular weight 47,500) both molecular weights determined by A. Tsugita from the amino acid composition, (personal communication)^2–5.