[Molecular biology of human herpesvirus 6: DNA replication and trans-activator genes]

HHV-6 genes and their functions that are unique and different from those of HCMV are summarized. HHV-6 encodes a HSV-1 UL9 homolog that is an origin-binding protein (OBP) essential for HSV-1 DNA replication, although HCMV has no clear homolog. The HHV-6 OBP binds to sequences with similarity to alpha-herpesvirus replication origin that lie within a genomic segment serving as an origin in transient assays. Consensus sequence for OBP binding, protein domain analyses and a model for OBP-origin interactions are described. HHV-6 encodes an AAV-2 rep homolog. Its transcript is expressed at low mRNA levels as a spliced transcript. The gene product suppresses both transformation by H.ras and transcription by HIV-1 promoters. HHV-6 specific transactivator gene DR7 exhibits malignant transforming activity and its protein binds to p53. Studies on IE-A locus and an HCMV UL69 homolog are also discussed.