THE DNA-SEQUENCE OF THE RK STRAIN OF HUMAN-HERPESVIRUS-7

The complete DNA sequence of human herpesvirus-7 (HHV-7) strain RK was determined following direct cloning of virion DNA fragments into a se quencing vector. The sequence was compared with the previously publish ed 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 reit erations, particularly in the ''telomeric'' reiterations located near the termini of the large direct repeat at the genome ends, and in a to tal 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 th ousands 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 counterpar ts, and all but 2 HHV-6 genes have HHV-7 homologues. Sequence comparis ons between HHV-7 and HHV-6 provided evidence that the protein-coding regions of 11 genes are expressed by splicing, (C) 1998 Academic Press .