The AP-1 binding site in the feline immunodeficiency virus long terminal repeat is not required for virus replication in feline T lymphocytes

1 Department of Veterinary Microbiology, Faculty of Agriculture, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113 2 Section of Serology, Institute of Immunological Science, Hokkaido University, Kita-ku, Sapporo 060 and 3 Department of Viral Oncology, Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto 606, Japan Sequences of 31 bp containing putative AP-1 and AP-4 binding sequences in the U3 region of the feline immunodeficiency virus (FIV) long terminal repeat (LTR) were deleted and the basal promoter activity of the LTR was measured by the chloramphenicol acetyltransferase (CAT) assay. The activity of the FIV LTR was reduced in Felis catus whole foetus 4 (fcwf-4) cells and Crandell feline kidney cells by this deletion. Cotransfection of murine c-Fos or c-Jun expression plasmids with the FIV LTR-CAT reporter plasmid into fcwf-4 cells revealed that FIV LTR could be activated by c-Fos but not c-Jun in the cells. The mutated LTR was introduced into an infectious molecular clone of FIV and the replication rate and the cytopathogenic activity of the mutant were compared with those of the wild-type in two feline CD4-positive T lymphoblastoid cell lines. It was found that the rate and activity of the mutant were almost the same as those of the wild-type. From these data, we conclude that the 31 bp fragment is important for achieving maximal expression of the FIV genome, but not required for the replication of FIV in feline T lymphocytes. Received 18 December 1992; accepted 19 March 1993.