Human herpesvirus 6 (HHV-6) and HHV-7 are closely related T-lymphotropic betaherpesviruses which share a common genomic organization and are composed of a single unique component (U) that is bounded by direct repeats (DR(L) and DR(R)). In HHV-6, a sequences have been identified at each end of the DR motifs, resulting in the arrangement aDR(L)a-U-aDR(R)a. In order to determine whether HHV-7 contains similar a sequences, we have sequenced the DR(L)-U and U-DR(R) junctions of HHV.7 strain JI, together with the DR(R) · DR(L) junction from the head-to-tail concatamer that is generated during productive virus infection. In addition, we have sequenced the genomic termini of an independent isolate of HHV-7. As in HHV-6, a (GGGTTA)(n) motif identical to the human telomeric repeat sequence (TRS) was identified adjacent to, but not at, the genome termini of HHV-7. The left genome terminus and the U-DR(R) junction contained a homolog of the consensus herpesvirus packaging signal, pac-1, followed by short tandem arrays of TRSs separated by single copies of a second 6-bp repeat. This organization is similar to the arrangement found at U-DR(R) in HHV-6 but differs from it in that the TRS arrays are considerably shorter in HHV-7. The right genome terminus and the DR(L)-U junction contained a homolog of the consensus herpesvirus packaging signal, pac-2, followed by longer tandem arrays of TRSs separated by single copies of either a 6-bp or a 14-hp repeat. This arrangement is considerably more complex than the simple tandem array of TRSs that is present at the corresponding genomic location in HHV-6 and corresponds to a site of both inter- and intrastrain heterogeneity in HHV-7. The presence of TRSs in lymphotropic herpesviruses from humans (HHV-6 and HHV-7), horses (equine herpesvirus 2), and birds (Marek's disease virus) is striking and suggests that these sequences may have functional or structural significance.
ASJC Scopus subject areas
- Insect Science