Distinct transcriptional and functional properties of the R transactivatorgene orf50 of the transforming herpesvirus Saimiri strain C488

The transformation-associated region of herpesvirus saimiri strains is vari able, whereas other parts of the virus genome are highly conserved. However , we observed considerable interstrain sequence divergence of the early vir al regulatory orf50 gene, which encodes the R transactivator, a homolog of Epstein-Barr virus BRLF1. The orf50 gene of strain C488 was transcribed at low abundance during lytic infection, whereas antisense transcripts were si multaneously expressed at high levels. A spliced variant, orf50a, was detec table by RT-PCR and RNase protection assays in stimulated C488-transformed, nonpermissive human T cells. In contrast to strain All, the short, unsplic ed orf50b form of C488 displayed complete transactivation capability on the orf6 and orf57 promoters. In summary, there are unexpected structural and functional differences between the orf50 genes of herpesvirus saimiri strai ns, which differ in their capability to transform human T lymphocytes. (C) 2000 Academic Press.