Sequence analysis and transcriptional activity of the LTR of OLV-CU1, a North American ovine lentivirus.

Although ovine lentiviruses have been described in the United States since the early part of this century, North American strains of sheep lentiviruses remain relatively uncharacterized at the molecular level. The LTR of a North American ovine lentivirus, OLV-CU1, was found to be closely related at the molecular and functional levels to visna virus, the Icelandic ovine lentivirus. Sequence analysis of the LTR revealed high identity to other ovine and caprine lentiviruses in key regulatory elements of the upstream promoter region (-25 to -115). However, the R region of the LTR was much less homologous. Transcriptional control of OLV-CU1 in transient transcriptional assays required a conserved putative AP-4 region and possibly an AP-1 like element in the upstream promoter region for moderate to high levels of transcription, much like visna virus. In contrast to visna virus, the downstream region beyond the transcriptional start site was required for virus-specific transactivation.