Affiliation:
1. Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California 94305-5124
Abstract
ABSTRACT
The
UL32 gene of human cytomegalovirus (CMV) encodes a prominent
betaherpesvirus-conserved virion tegument protein, called pp150 (basic
phosphoprotein/ppUL32), that accumulates within a cytoplasmic inclusion
adjacent to the nucleus at late times during infection. Using a UL32
deletion mutant (ΔUL32-BAC) (where BAC is bacterial artificial
chromosome), we demonstrate that pp150 is critical for virion
maturation in the cytoplasmic compartment. Cotransfection of a pp150
expression plasmid with ΔUL32-BAC DNA led to complementation of
the replication defect with focus formation due to secondary spread.
Deletion of the amino terminus of pp150 or disruption of the
betaherpesvirus conserved regions, CR1 and CR2, revealed these regions
to be critical for replication. In contrast, deletion of the carboxyl
terminus only partially compromised maturation while disruption of
glycosylation sites had no effect. An African green monkey CMV UL32
homolog complemented ΔUL32-BAC replication but murine CMV M32
failed to complement, consistent with evolutionary divergence of rodent
and primate cytomegaloviruses. Infection with ΔUL32-BAC showed
normal expression of all kinetic classes of viral genes and replication
of viral DNA, with accumulation of viral DNA-containing particles in
the cytoplasm; however, mutant virus did not spread to adjacent cells.
In contrast to this block in virion infectivity, cell-to-cell transfer
of pp65-containing particles was observed, suggesting that release of
dense bodies continued in the absence of pp150. These observations
demonstrate that pp150 is critical for virion egress, possibly at the
stage of final
envelopment.
Publisher
American Society for Microbiology
Subject
Virology,Insect Science,Immunology,Microbiology