Characterization of transcripts expressed from human herpesvirus 6A strainGS immediate-early region BU16-U17 open reading frames

Several gene fragments of human herpesvirus 6 (HHV-6) have been shown to ac tivate the human immunodeficiency virus (HM type 1 long terminal repeat (LT R). An open reading frame (ORF) designated B701 (Y. Geng, B. Chandran, S. F . Josephs, and C. Wood, J. Virol. 66:1564-1570, 1992), found within a 22-kb HHV-6A strain GS [HHV-6A(GS)] genomic fragment and a 3.8-kb SalI subfragme nt, was shown to activate the HIV LTR. B701, also known as HRV-6 U16, is lo cated in the immediate-early B (IE-B) region of the genome. The sequence of the 3.8-kb genomic fragment of HHV-6A(GS) is nearly identical to the publi shed sequence of HHV-6A strain U1102, with minor differences. The HHV-6A(GS ) B701 ORF (U16) was used to screen an HHV-6A(GS) cDNA library, and two dif ferent but overlapping cDNAs were identified. These cDNAs represent differe ntly spliced transcripts ending at different polyadenylation signals. The O RFs included in the cDNAs are positionally homologous to the human cytomega lovirus (HCMV) UL36 ORF. The ORF in one cDNA was generated by splicing toge ther in frame OPFs U17 and U16, and the second cDNA included ORFs U16 and U 15. A third differentially spliced cDNA (U16+), was identified by 5 ' rapid amplification of cDNA ends. The predicted protein was identical to the U16 portion of the U17/U16 spliced gene product but did not include the U17 po rtion. 5 ' -extension analyses of the mRNAs demonstrated that at least two potential transcription initiation sites were used to express the transcrip ts encoding U17 and U16 gene products. Single-stranded U16 and U17 gene-spe cific RNA probes hybridized with at least five RNA species from infected ce lls and demonstrated that the expression of these transcripts was different ially regulated. The U17/U16 spliced gene products were expressed at IE tim es after infection, but a multiply spliced gene product encoded by U16 was expressed as a late gene. The UI7/U16 and the U16+ gene products transactiv ated the HIV LTR. Thus, while there are similarities to the HCMV UL36-UL38 gene family, some of the IE-B U17/U16 transcripts are unique to HHV-6.