Cytoplasmic envelopment of human cytomegalovirus requires the postlocalization function of tegument protein pp28 within the assembly compartment.
The assembly of herpesvirus remains incompletely defined due to the structural complexity of these viruses. Although the assembly of the capsid of these large DNA viruses is well studied and reasonably well conserved for all members of this diverse family of viruses, the cytoplasmic processes of tegumentation and envelopment are not well understood. The virion of the largest human herpesvirus, human cytomegalovirus (HCMV), contains over 70 virus-encoded proteins that are incorporated during a nuclear and cytoplasmic phase of assembly. Envelopment of this virus requires the function of at least one tegument protein, pp28, the product of the UL99 open reading frame. However, the role of pp28 in the envelopment of HCMV remains undefined. We have generated a pp28 mutant virus that encodes only the first 50 amino acids (aa) of this 190-aa virion protein. This virus is replication impaired and is defective in virus assembly. Characterization of both intracellular and extracellular virions from cells infected with this viral mutant indicated that the decrease in production of infectious virus was secondary to a defect in envelopment and the accumulation of tegumented, noninfectious intracellular particles. Image analysis using fluorescence recovery after photobleaching indicated that the pp28 mutant protein encoded by this virus failed to efficiently accumulate in the virus assembly compartment (AC). Our results suggest that pp28 must accumulate in the AC for efficient envelopment of the particle and provide evidence for a direct role of this tegument protein in the late stages of assembly, such as envelopment.
Seo
Jun-Young
JY
Department of Microbiology, University of Alabama School of Medicine, and Department of Pediatrics, Children's Hospital, 1600 7th Ave. South, Birmingham, AL 35233, USA.
Britt
William J
WJ
D000595:Amino Acid Sequence; D002467:Cell Nucleus / Q000821:virology; D003062:Codon; D003587:Cytomegalovirus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism / Q000821:virology*; D005347:Fibroblasts / Q000378:metabolism; D015967:Gene Expression Regulation, Viral; D049452:Green Fluorescent Proteins / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D008854:Microscopy, Electron; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000096:biosynthesis* / Q000502:physiology*; D013997:Time Factors; D014764:Viral Proteins / Q000096:biosynthesis* / Q000502:physiology*
D003062:Codon; D010750:Phosphoproteins; D014764:Viral Proteins; C070746:human cytomegalovirus protein pp28; D049452:Green Fluorescent Proteins