The Kinetics of Protein Synthesis in Pseudorabies Virus
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Pseudorabies virus (PrV) is a member of the herpesvirus family and is molecularly similar to herpes simplex virus (HSV). The glycosalated proteins as well as the non-glycosalated proteins of PrV are thought to be temporally regulated in a cascade pattern similar to that described for HSV-I. Proteins are classified as α, β, β8, and 8 proteins based on their kinetics and requirements for synthesis. PrV gX, a major PrV glycoprotein, was characterized as a PrV β protein, based on the kinetics of protein synthesis in 5 virus strains. The kinetics of gX synthesis were studied in the parent strain, PrV HR, when gX synthesis is directed by its own promoter sequence. gp50 synthesis was studied in the recombinant virus PrV x50, when gp50 synthesis is directed by the gX promoter sequence. tPA synthesis was also studied in the recombinant virus PrV tPA, when tPA synthesis is directed by the gX promoter sequence. tPA or tissue plasminogen activator, a model gene was inserted downstream from the gX promoter sequence to examine PrV as a vector for foreign gene expression. gX in PrV HR, gp50 in PrV x50, and tPA in PrV tPA all were expressed as early as 2 hours postinfection, suggesting that gX is a PrV β protein. The data also suggests that some inherent difference in the stability of the mRNA in the infected cell could explain the appearance of gX throughout infection and the disappearance of both gp50 and tPA by 8 hours of infection, when regulated by the gX promoter sequence. The kinetics of gX synthesis were also studied in the recombinant viruses HSVgX and HSVSgX. gX synthesis in HSVgX, when gX synthesis is regulated by its own promoter sequence, strongly resembles gX synthesis in PrV HR. This supports the classification of gX as a PrV β protein. gX synthesis in HSVSgX, when gX is regulated by the ICPS (major capsid protein) promoter sequence, strongly resembles HSV ICPS synthesis, suggesting that gX synthesis is strongly influenced by the HSV ICPS β8 promoter sequence.