Proteolytic cleavage of the amino terminus of the U(L)15 gene product of herpes simplex virus type 1 is coupled with maturation of viral DNA into unit-length genomes.
The U(L)15 gene of herpes simplex virus type 1 (HSV-1), like U(L)6, U(L)17, U(L)28, U(L)32, and U(L)33, is required for cleavage of concatameric DNA into genomic lengths and for packaging of cleaved genomes into preformed capsids. A previous study indicated that the U(L)15 gene encodes minor capsid proteins. In the present study, we have shown that the amino-terminal 509 amino acids of the U(L)15-encoded protein are sufficient to confer capsid association inasmuch as a carboxyl-terminally truncated form of the U(L)15-encoded protein with an M(r) of approximately 55,000 readily associated with capsids. This and previous studies have shown that, whereas three U(L)15-encoded proteins with apparent M(r)s of 83,000, 80,000, and 79,000 associated with wild-type B capsids, only the full-length 83,000-M(r) protein associated with B capsids purified from cells infected with viruses lacking functional U(L)6, U(L)17, U(L)28, U(L)32, and U(L)33 genes (B. Salmon and J. D. Baines, J. Virol. 72:3045-3050, 1998). Thus, all viral mutants that fail to cleave viral DNA into genomic-length molecules also fail to produce capsid-associated U(L)15 80,000- and 79,000-M(r) proteins. In contrast, the 80,000- and 79,000-M(r) proteins were readily detected in capsids purified from cells infected with a U(L)25 null virus that cleaves, but does not package, DNA. The conclusion that the amino terminus of the 83,000-M(r) protein is truncated to produce the 80,000- and/or 79,000-M(r) protein was supported by the following observations. (i) Whereas the C termini of the 83,000-, 80, 000-, and 79,000-M(r) proteins are identical, immunoreactivity dependent on the first 35 amino acids of the U(L)15 83,000-M(r) protein was absent from the 80,000- and 79,000-M(r) proteins. (ii) The 79,000- and 80,000-M(r) proteins were detected in capsids from cells infected with HSV-1(U(L)15M36V), an engineered virus encoding valine rather than methionine at codon 36. Thus, initiation at codon 36 is unlikely to account for production of the 80,000- and/or 79, 000-M(r) protein. Taken together, these data strongly suggest that capsid-associated U(L)15-encoded protein is proteolytically cleaved near the N terminus and indicate that this modification is tightly linked to maturation of genomic DNA.
Salmon
B
B
C5143 Veterinary Education Center, Department of Microbiology and Immunology, Cornell University, Ithaca, New York 14853, USA.
Nalwanga
D
D
Fan
Y
Y
Baines
J D
JD
D004279:DNA, Viral / Q000235:genetics*; D016679:Genome, Viral; D018259:Herpesvirus 1, Human / Q000502:physiology*; D006801:Humans; D014764:Viral Proteins / Q000235:genetics*; D019065:Virus Assembly / Q000235:genetics
D004279:DNA, Viral; D014764:Viral Proteins; C069185:DNA cleavage and packaging proteins, Herpesvirus