Varicella-Zoster VirusOpenReading Frame10Protein, the HerpesSimplex VirusVP16Homolog,Transactivates Herpesvirus Immediate-Early GenePromoters

Thevaricella-zoster virus (VZV)open reading frame10(ORF10) protein isthehomologoftheherpes simplex virus type1(HSV-1) protein VP16.These aretwovirion tegumentproteins thathaveextensive amino acid sequenceidentity intheir amino-terminal andmiddle domains. ORF10,however, lacks theacidic carboxy terminus whichiscritical fortransactivation byVP16.Earlier studies showed that VZV ORF10doesnotform a tertiary complex withtheTAATGARAT regulatory element (where R isa purine) withwhichHSV-1VP16 interacts, suggesting thatORFIOmay nothavetransactivating ability. Usingtransient-expression assays,we showthatVZV ORF10isabletotransactivate VZV immediate-early (IE) gene (ORF62) andHSV-1IEgene (ICP4andICPO)promoters. Furthermore, cell lines stably expressing ORF10complement theHSV-1mutant in1814, whichlacks thetransactivating function ofVP16,andenhance thedenovo synthesis ofinfectious virus following transfection ofHSV-1virion DNA.Theseresults indicate thatORFIO,like its HSV-1homolog VP16, isatransactivating protein despite theabsence ofsequencessimilar totheVP16carboxy-terminal domain. The transactivating function oftheVZV ORF10tegument protein may becritical forefficient initiation ofviral infection.