Characterization of endogenous and recombinant proviral elements of a highly tumorigenic AKR cell line.

As an approach to evaluating the contribution of classes of endogenous viral sequences to leukemogenesis, a genomic library was prepared from the highly tumorigenic AKR SL12.3 cell line and screened for env-containing proviruses. An extensive battery of virus-derived probes and specific oligonucleotide probes were used to segregate 83 positive clones into related groups. The nonecotropic endogenous retroviruses were identified as members of the polytropic, modified polytropic, or xenotropic groups. At least three unique xenotropic proviruses were detected that differed from the published xenotropic sequence within a variable region of the 5' portion of env. Changes among the xenotropic proviruses included relative insertions and/or deletions that maintain an open reading frame and hence the potential to encode viable envelope gene products. Several recombinant viruses were also detected. Recombination was not random and primarily involved the formation of mink cell focus-inducing class I retroviruses via recombination between polytropic elements and ecotropic virus. One other recombinant was detected which contained ecotropic virus sequences in the 5' region encoding p15 of an otherwise xenotropic provirus. An interesting observation was the finding that certain clones contained more than one provirus within the average 20-kb cloned insert. This would not be expected if integration were totally random. The de novo recombinant proviruses identified here provide a series of potential candidates to be evaluated for their contribution to the tumorigencity of the SL12.3 cell line.

Comparison of two host cell range variants of feline immunodeficiency virus.

Two molecular clones of feline immunodeficiency virus were compared. The first clone, 34TF10, was from a Petaluma, Calif., isolate; the second, PPR, was isolated from a cat in the San Diego, Calif., area. The cats from which the isolates were obtained suffered from chronic debilitating illnesses. The two molecular clones differed in their in vitro host cell range. The 34TF10 clone infected the Crandall feline kidney and G355-5 cell lines, but replicated less efficiently on feline peripheral blood leukocytes. In contrast, the PPR clone productively infected the primary feline peripheral blood leukocytes but not Crandall feline kidney or G355-5 cells. The 34TF10 and PPR clones had an overall sequence identity of 91%. The env gene was the least conserved (85% at the amino acid level). Additionally, the potential open reading frame for a Tat-like protein, ORF 2, contained a stop codon in the 34TF10 isolate which was not found in the PPR clone. This truncation did not prevent in vitro or in vivo replication of 34TF10. Two splice acceptor sites were identified in the 34TF10 clone. One was 5' to the beginning of the putative tat open reading frame, and the other was 5' to the putative vif product. Both of these acceptor sites were conserved in the PPR clone. The long terminal repeats of the viruses were 7% divergent between the two clones, with a lack of conservation in putative NF-kappa B, LBP-1, and CCAAT enhancer-promoter sites.

Nucleotide sequence and genomic organization of feline immunodeficiency virus.

An infectious molecular clone of the Petaluma strain of feline immunodeficiency virus (FIV) was isolated from a recombinant bacteriophage library containing genomic DNA prepared from FIV-infected Crandall feline kidney (CRFK) cells. The integrated provirus has a total length of 9472 base pairs. Three long open reading frames corresponding to GAG, POL, and ENV gene coding frames are evident. In addition, an open reading frame overlaps the 3' end of POL, in the region that encodes viral infectivity factor in the primate viruses. Several short open reading frames are present in the intergenic region between POL and ENV and within ENV, which may serve as exons for production of TAT and REV equivalents in FIV. Alignment of the predicted amino acid sequences of the FIV proteins with those of other lentiviruses indicates that FIV did not arise recently from any other characterized lentivirus.