The complete DNA sequence of human herpesvirus-7 (HHV-7) strain RK was determined following direct cloning of virion DNA fragments into a sequencing vector. The sequence was compared with the previously published complete sequences of HHV-7 strain JI and human herpesvirus-6 (HHV-6) strain U1102. Despite a very close relationship between the two HHV-7 strains, differences are apparent in regions containing tandem reiterations, particularly in the "telomeric" reiterations located near the termini of the large direct repeat at the genome ends, and in a total of 179 additional positions distributed throughout the genome (i.e., about one nucleotide difference per kbp). This extent of divergence implies that the two strains arose from an ancestral virus several thousands of years ago. Differences that affect coding potential do not cluster in particular protein-coding regions, indicating that specific HHV-7 genes have not been measurably subject to unusual evolutionary pressures since divergence. Reassessments of genetic content indicated that the HHV-7 genome contains 84 different genes, whereas the HHV-6 genome contains 85. All HHV-7 genes but 1 have direct HHV-6 counterparts, and all but 2 HHV-6 genes have HHV-7 homologues. Sequence comparisons between HHV-7 and HHV-6 provided evidence that the protein-coding regions of 11 genes are expressed by splicing.

SUMMARYThe genome of an Australian isolate of equine herpesvirus type 1 (equine abortion virus) has been analysed using the restriction endonucleases EcoRI, BglII and BamHI, and a physical map constructed. Terminal fragments were identified by exonuclease treatments, and linkage of fragments was deduced by a combination of single-and double-digest experiments and cross-blot hybridizations. The genome has a mol. wt. of 100 x 10 6 and is comprised of a short unique region bounded by repetitive sequences, which is present in both orientations in approximately equal amounts in the DNA population, and a long unique region existing in only one orientation.

The linear duplex DNA molecule of varicella‐zoster virus is 120 000 bp in size and has the sequence arrangement UL‐IRS‐US‐TRS, where UL and US are unique sequences and IRS and TRS are inverted repeats flanking US. The primary structure of the cloned SstI g DNA fragment containing US (5232 bp) and adjacent portions of IRS and TRS (426 bp of each) was determined, and the following model for genetic expression was derived from an analysis of the sequence. The region specifies four mRNAs encoding primary translation products with mol. wts. of 11, 44, 39 and either 74 or 70 kd. The 39‐and 70‐kd proteins have primary structures characteristic of membrane proteins. The mRNAs encoding the 11‐ and 74/70‐kd proteins extend from opposite sides of US into IRS/TRS, thus sharing a common 3′ terminus. These proteins do not share a common carboxy terminus because the coding region for the 11‐kd protein terminates at the junction between US and IRS, whereas that for the 74/70‐kd protein extends into TRS. The analysis affirms the hypothesis that the extent of inverted repeats in herpesvirus genomes is primarily a result of constraints imposed by adjacent protein coding sequences.

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