HUMAN HERPESVIRUS 6A TS SUPPRESSES BOTH TRANSFORMATION BY H-RAS AND TRANSCRIPTION BY THE H-RAS AND HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 PROMOTERS

Human herpesvirus 6 strain U1102 (HHV-6A) was shown to contain a 1,473 -bp functional transformation suppressor gene (ts). ts exhibited 24% i dentity and 51% similarity to adeno-associated virus type 2 Rep68/78. Like adeno-associated virus type 2 Rep68/78, HHV-6A ts suppressed H-ra s transformation of NIH 3T3 cells. Suppression of H-ras transformation was eliminated by translation termination linker mutation at amino ac id 25, 125, or 245. These data indicated the importance of the C-termi nal portion of the ts protein. H-ras transformation was suppressed by ts only when H-ras was expressed by its endogenous H-ras promoter and not when it was expressed by the heterologous murine osteosarcoma viru s long terminal repeat (LTR). Furthermore, ts suppressed chloramphenic ol acetyltransferase (CAT) activity when the CAT gene was expressed fr om the H-ras promoter but not the murine osteosarcoma virus LTR promot er. Taken together, the data showed that ts suppressed H-ras transform ation at the level of the H-ras promoter. To further identify the inte raction of fs with transcriptional regulatory elements, the human immu nodeficiency virus type 1 (HIV-1) LTR was used. This promoter was sele cted because it has well-defined transcriptional regulatory elements f or both basal and activated transcription, because its activity is inh ibited by the Rep68/78 gene, and because both HHV-6 and HIV-1 naturall y infect CD4(+) T cells in vivo and have been shown to infect the same cell in vitro. fs suppressed expression from both wild-type and upstr eam mutant HIV-1 LTR-CAT constructs. However, downstream HIV-1 TAR mut ations reversed ts suppression, indicating that TAR is one of the crit ical elements involved. The data presented demonstrated that HHV-6A ts functionally suppressed H-ras transformation and HIV-1 LTR expression and thus that it may be useful in future gene therapy.