Localization of minor protein components of the head of bacteriophage T4

Abstract

The bacteriophage T4 capsid contains a number of minor proteins that are required for head assembly but whose detailed function and position in the head are unknown. We have found that by systematically varying the conditions of extraction, some of these minor proteins can be removed while the main capsid structure is left substantially intact. Electron microscopic examination of the residual capsids showed that the extraction ofthe product of gene 20 is correlated with the loss of a plug that distinguishes one vertex position (presumably the tail attachment site) from the others. Extraction of the product of gene 24 is correlated with the loss of the other 11 (nonproximal) vertexes of the capsid. We further show that antibody to P24 binds specifically to the nonproximal vertexes of both T4 preheads and T4 phages. On the basis of our findings, we suggest that P20 is located at or near the tail attachment site ofthe capsid, whereas P24 forms the 11 nonproximal vertexes of preheads and P24* forms the nonproximal vertexes of the mature head.

Isolation and characterization of bacteriophage T4 mutant preheads

“…Mutations in genes 20, 22, and 40 can cause P23 to assemble into polyheads, but do not make struc-tures with the 15,5 folding of preheads. We have presented evidence (18) that all of the P20 of the capsid is present at the proximal vertex, because it can be removed together with a structure at one of the apical vertices under conditions which leave the other vertices intact. Our micrographs of purified preheads show that they have a similar structure at the vertex which is attached to the bacterial membrane.…”

“…Gene 21 codes for a precursor to the T4 protease (23), and apparently the tsP21 zymogen cannot be activated after a shift to the permissive temper-ature because none of the maturation cleavages takes place after such a shift (13,16). Gene 24 codes for the vertex protein of the prehead and capsid (18). Unlike the temperature-sensitive (ts) gene 21 mutants, many of the ts gene 24 mutants are temperature reversible (3).…”

Prohead core of bacteriophage T4 can act as an intermediate in the T4 head assembly pathway

“…Besides these particles, we observed tubular structures which obviously represented shelled cores that were elongated by continuous shell growth. gp2O has been localized at the proximal vertex (11), and it therefore appears to be essential for correct initiation of shell assembly. However, even in the absence of gp2O, gp23 was assembled and showed a strong affinity for the cores.…”

“…Infections of E. coli B with mutants carrying three different amber mutations in gene 20 show a similar phenotype (M. Maeder and F. Traub, unpublished). Since gp2O is probably localized at the proximal vertex (11), it may assemble around the core neck and thereby anchor the prohead to the membrane. Indeed, mutant 20(amE481) 23 (amHll) infections of E. coli B show naked cores detached from the membrane (18).…”

On the Structure of the Scaffolding Core of Bacteriophage T4

“…Closed structures cannot be formed solely by a hexagonal lattice; in order to form a closed structure, these viruses have 12 pentamers which replace hexamers at the vertices of the polyhedron. While in many viruses, the pentamers are formed from the same protein as the hexamers, in T4 the pentamers are believed to be formed from gp24 (M uller-Salamin et al, 1977). A capsomere will mean either a hexamer or a pentamer in the shell.…”