Temporal mapping of transcripts in human herpesvirus-7.

Transcription of human herpesvirus-7 (HHV-7) in cultures of productively infected T-cells was studied. Transcription of HHV-7 was regulated by the typical herpesvirus cascade in which alpha, beta and gamma genes are sequentially transcribed. Transcripts of U10, U14, U18, U31, U39, U41, U42, U53, U73 and U89/90 were detected 3 h after infection and were not inhibited by the absence of protein synthesis and therefore were alpha functions. U19 and U18/20 were beta genes; their transcription was inhibited by cycloheximide but not by phosphonoacetate, an inhibitor of DNA synthesis. U60/66 and U98/100 were gamma genes since their spliced transcripts were not detected in cells treated with phosphonoacetate. HHV-7 transcription was regulated by complex mechanisms, which involve the temporal coordinated activation of specific viral promoters and post-transcriptional processing. Splice mechanisms were also temporally regulated. Transcription of U89/90 pre-mRNA and splice took place simultaneously in the immediate-early phase. On the other hand, U16/17 pre-mRNA was synthesized with typical alpha kinetics, but the spliced product was regulated as a beta function. Likewise, the primary transcripts of U60/66 and U98/100 were alpha and beta, respectively, but both spliced products were synthesized in the late phase of virus replication. Finally, HHV-7 supported a bona fide latent infection in the adult population, since viral transcripts were not detected in peripheral blood mononuclear cells of healthy donors infected with HHV-7.