Regulation of pseudorabies virus gG glycoprotein gene promoter independently of pseudorabies immediate early IE180 protein.

The pseudorabies virus (PRV) glycoprotein known as gG is generally regarded as an early protein, and the immediate early IE180 protein regulates its expression during infection. This study, however, provides evidence that although induction by IE180 is observed, the expression of a marker protein (EGFP), or gG itself, under the control of the gG promoter, can also occur independently of the expression of IE180. This result was demonstrated both with transient transfection assays using plasmids and with viral infections. In transient transfections, the expression under control of the gG promoter depends on the cell type and surprisingly, can be 1.3-fold higher than the expression under the control of the IE180 promoter in Hela Tet-Off cells. Recombinant PRV S3 was constructed by replacing gE in the PRV genome with a chimeric transgene, expressing EGFP under the control of the gG promoter. In PK15 cells infected with NIA-3 wild-type virus or with S3 recombinant virus, expression of gG PRV mRNA (or EGFP mRNA) under the control of the gG promoter in the presence of cycloheximide was detected by RT-PCR. This again indicates that some basal expression was produced in infected cells independently of IE180. This expression was augmented by IE180 protein in both plasmid transfections and viral infections.