INFLUENCE OF ORF2 ON HOST-CELL TROPISM OF FELINE IMMUNODEFICIENCY VIRUS

Feline immunodeficiency virus (FIV) is a lentivirus associated with an immunodeficiency syndrome of the domestic cat. A short open reading f rame (ORF2), of unknown function, is present in all FIV isolates. We h ave investigated the role of ORF2 in determining the cell tropism of t wo infectious molecular clones of FIV. FIV-PPR is able to productively infect feline peripheral blood leukocytes (PBLs) and a T lymphocyte c ell line (MCH5-4), but not a feline astrocyte cell line (G355-5) or Cr andell feline kidney cells (CrFK). In contrast, FIV-34TF10 is able to productively infect G355-5 and CrFK cells, but not PBLs or MCH5-4 cell s. The major difference in these FIV clones is that ORF2 in FIV-PPR is capable of encoding a 79-amino-acid peptide, whereas there is a stop codon in ORF2 after 43 amino acids in FIV-34TF10. We performed site-di rected mutagenesis to change the stop codon (TGA) in FIV-34TF10 to a t ryptophan (TGG), the amino acid present at this location in FIV-PPR. F IV-34TF10 with ORF2 repaired (FIV-ORF2rep) productively infected PBLs, MCH5-4 cells, and primary macrophages, as well as CrFK and G355-5 cel ls, indicating that a protein encoded by ORF2 plays a role in determin ing the host cell tropism of FIV. ORF2 contains hydrophobic, acidic, a nd leucine-rich domains similar to those shown to be important for tra nsactivating proteins of other lentiviruses, Coexpression of a plasmid expressing the ORF2 gene product with another construct expressing th e chloramphenicol acetyl transferase (CAT) gene driven by the FIV LTR, resulted in transactivation of CAT expression in both feline and huma n cells. (C) 1996 academic Press, Inc.