Structure of transcripts and proteins encoded by U79-80 of human herpesvirus 6 and its subcellular localization in infected cells

We analyzed the U79-80 gene of human herpesvirus 6 (HHV-6), which is predic ted to be a positional homolog of the UL112-113 gene of human cytomegalovir us (HCMV). The U79-80 gene encoded a family of nuclear proteins of 36, 41, 44, and 59 kDa. These proteins had common amino termini and were generated by complex alternative splicing. Transcripts from U79-80 appeared as early as 3 h postinfection and could be detected in the presence of phosphonoform ate. U79-80 proteins were seen as early as 8 h postinfection and could be d etected in the presence of phosphonoformate but not in the presence of cycl oheximide combined with actinomycin D treatment. The U79-80 proteins were l ocalized to the nucleus of infected cells, where they were detected as a sp eckled or punctuate pattern. Moreover the U79-80 proteins colocalized with the components of the viral DNA replication machinery and appeared to distr ibute adjacent to or touching nuclear domain 10, where viral DNA replicatio n occurs. From the sequence analysis of genomic DNA, the predicted amino ac id similarity between U79-80 and UL112-113 was lower than between other gen es, but the characteristics of the transcripts and proteins encoded by U79- 80 were similar to those of UL112-113. These results suggest that the U79-8 0 proteins have a role in viral DNA replication and are functional homologu es of the UL112-113 proteins, (C) 2000 Academic Press.