HIV F/3' orf encodes a phosphorylated GTP-binding protein resembling an oncogene product

Apart from the retroviral gag, pol and env1,2, the HIV genome contains the F (3'orf) gene which encodes a polypeptide of 206 amino acids which is myristylated at the N-terminal and whose function is unknown3,4. We have expressed the F gene in Escherichia coli and from a recombinant vaccinia virus, VVTGfHIV. The F-protein produced in VVTGfHIV-infected mammalian cells is myristilated, and is phosphorylated by protein kinase C at a residue close to the N-terminus like pp60-src (ref. 5). Purified bacterial F-protein also shows the GTPase, auto-phosphorylation and GTP-binding activities reported for the ras gene product6,7. Furthermore, we show that expression of F in a CD4+ cell line down-regulates the CD4 (T4) antigen. These results suggest that F is important in the pathophysiology of AIDS (aquired immune deficiency syndrome).