Human cytomegalovirus UL99-encoded pp28 is required for the cytoplasmic envelopment of tegument-associated capsids.
The human cytomegalovirus UL99-encoded pp28 is a myristylated phosphoprotein that is a constituent of the virion. The pp28 protein is positioned within the tegument of the virus particle, a protein structure that resides between the capsid and envelope. In the infected cell, pp28 is found in a cytoplasmic compartment derived from the Golgi apparatus, where the virus buds into vesicles to acquire its final membrane. We have constructed two mutants of human cytomegalovirus that fail to produce the pp28 protein, a substitution mutant (BADsubUL99) and a point mutant (BADpmUL99), and we have propagated them by complementation in pp28-expressing fibroblasts. Both mutant viruses are profoundly defective for growth in normal fibroblasts; no infectious virus could be detected after infection. Whereas normal levels of viral DNA and late proteins were observed in mutant virus-infected cells, large numbers of tegument-associated capsids accumulated in the cytoplasm that failed to acquire an envelope. We conclude that pp28 is required for the final envelopment of the human cytomegalovirus virion in the cytoplasm.
Silva
Maria C
MC
Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544-1014, USA.
Yu
Qian-Chun
QC
Enquist
Lynn
L
Shenk
Thomas
T
D002213:Capsid / Q000502:physiology*; D002478:Cells, Cultured; D003587:Cytomegalovirus / Q000502:physiology*; D003593:Cytoplasm / Q000821:virology*; D006801:Humans; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014759:Viral Envelope Proteins / Q000378:metabolism; D014763:Viral Matrix Proteins / Q000378:metabolism; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology*; D019065:Virus Assembly; D014779:Virus Replication
D010750:Phosphoproteins; D014759:Viral Envelope Proteins; D014763:Viral Matrix Proteins; D014764:Viral Proteins; C065418:cytomegalovirus matrix protein 65kDa; C040495:glycoprotein B, Simplexvirus; C070746:human cytomegalovirus protein pp28