TEMPORAL MAPPING OF TRANSCRIPTS IN HERPESVIRUS-6 VARIANTS

To define the molecular features characteristic of the early stages of infection of lymphocytes with human herpesvirus 6 (HHV-6) variant A o r B, we studied the temporal regulation of expression of selected sets of viral genes. Thus, U42, U94, U89-U90, U73, and U39 are alpha genes since their transcripts (i) were made in the presence of inhibitors o f protein synthesis and (ii) were detected 3 h after infection of untr eated cells. U41, U53, U31, and U19 are beta genes since their express ion is inhibited by cycloheximide but not by phosphonoacetate, an inhi bitor of DNA synthesis. U100 is a gamma gene since its spliced transcr ipt encoding the structural glycoprotein gp82/105 was first detected 1 6 h after infection of untreated cells but could not be detected in ce lls treated with phosphonoacetate, HHV-6 variants differ in the transc ription patterns of their genes. U16-U17 originates a splice transcrip t and is regulated as alpha in HHV-6B and as beta in HHV-6A. U91 gener ates two transcripts, amplified as 476- and 374-bp PCR fragments. The 476-bp fragment is alpha in HHV-6A-infected cells but beta in HHV-6B-i nfected cells. Conversely, the 374-bp fragment is beta in HRV-6A-infec ted cells and or in HHV-6B-infected cells. Furthermore, the spliced pr oduct of U18-U19-U20 (526 bp) is beta in HHV-6A-infected cells, but on ly a partially spliced form (1.9 kb) was detected at late stages of in fection in HHV-6B, HHV-6 transcription was also studied in nonproducti ve lymphoid cells, and the same transcription pattern detected during lytic infection was observed. Also, HHV-6 variants maintain the differ ences in U91, U16-17, and U18-U19-U20, We conclude that, as expected f rom the sequencing data, gene expression is generally similar in HHV-6 variants. However, transcription of selected genes in HHV-6A and HHV- 6B differs with respect to temporal regulation and splicing pattern. F urthermore, the identification of viral functions expressed during the different stages of lytic replication suggests that reverse transcrip tion-PCR for HHV-6 genes is a useful diagnostic approach to differenti ate between latent and productive HHV-6 infection.