Unique Genetic Regions
There are at least two regions of the HTLV-III virus—called sor and 3’ orf—that have no direct counterpart in any other retrovirus studied to date. According to the Nature report, sor may be a remnant of a former envelope gene; 3’ orf may not be a gene at all, since only one of the two HTLV-III isolates that were sequenced contained such a region.
The nucleotide sequences of two isolates studied by the American group differed by about 1 percent, Dr. Haseltine told GEN. Similarly, the genetic analysis of the LAV isolate by the French group—which appears in the January issue of Cell—differed from either of the American sequences by about 1 percent.
“I think the fundamental thing is that they [HTLV-III and the LAV] are the same agent—there’s no doubt any longer,” said Dr. Haseltine.
Chiron Corporation has analyzed a virus known as ARV (AIDS-Related Virus) and expects to publish their results in the February 1 issue of Science. Dr. Haseltine said, based on discussions he has had with members of the Chiron group, that the ARV is yet another isolate of the HTLV-III virus.
In related work, the American team claims that the HTLV-III virus, like the other HTLV viruses, alters cells by affecting the mechanism by which genes are transcribed, a phenomenon called trans-acting transcriptional regulation (TAT). They suggest that the common structural and functional features of the HTLV viruses—the presence of the lor gene and the TAT phenomenon—set the HTLV family of viruses apart from other retroviruses.