Protein cleavage during virus assembly: characterization of cleavage in T4 phage.

Abstract

Since the reports of cleavage of viron precursor proteins during the maturation of poliovirus and bacteriophage T4, proteolytic reactions have been reported during the life cycles of numerous animal and bacterial viruses. During the maturation of the head of bacteriophage T4, four proteins have been shown, by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate, to increase in mobility suggesting a decrease in molecular weight. They are: P23, the major capsid protein, P24, a minor capsid protein, IP-III and B1 (or alt), internal proteins of the mature virion. A fifth protein, P22, a core component of the virus prohead, disappears from sodium dodecyl sulphate gels in pulse-chase experiments; presumably it is cleaved to small fragments (Hosoda & Levinthal, 1968; Laemmli; 1970; Kellenberger & Kellenberger-van der Kamp, 1970; Dickson et al., 1970; Coppo et al., 1973). Celis et al. (1973) demonstrated that the reduction of mobility of P23 is due to cleavage of the precursor protein, and that it results in the loss of the N-terminal portion of the precursor. For all of the T4 precursor proteins excpet P22, the apparent cleavage results in the loss of less than 20% of the molecule, the remaining 80% being incorporated into the virus intact.