COMPARISON OF A 20 KB REGION OF HUMAN HERPESVIRUS 6B WITH OTHER HUMANBETAHERPESVIRUSES REVEALS CONSERVED REPLICATION GENES AND ADJACENT DIVERGENT OPEN READING FRAMES

The sequence of a 20.15 kb region from human herpesvirus 6 variant B ( HHV-6B) strain Z29 is described (GenBank accession number L14772). Det erminations of protein homologies for seventeen predicted gene product s revealed HHV-6B homologs of six proteins well-conserved both in gene tic context and amino acid sequence throughout the alpha-, beta-, and gammaherpesvirus subfamilies. These include proteins involved in viral DNA replication, packaging and nucleotide metabolism, and conserved p roteins of undefined function. The close evolutionary relationship of the human betaherpesviruses, HHV-6B, HHV-6A, HHV-7 and human cytomegal ovirus (HCMV) was confirmed by identification of several protein seque nces encoded only by these viruses, including homologs of the HCMV ear ly phosphoprotein family and a series of HCMV open reading frames pred icted to encode glycoprotein exons. Homologs of essential HSV-1 replic ation proteins, UL8 and UL9, were also identified. Downstream from the conserved replication locus, each betaherpesvirus contains a region o f divergent, small open reading frames. The evolution of this region a nd its potential use in the development of a viral vector system are d iscussed.