Molecular cloning of the closed circular provirus of human T cell leukaemia virus type I: a new open reading frame in the gag-pol region.

A DNA clone of human T cell leukaemia virus type I (HTLV-I) was isolated from extrachromosomal closed circular copies in chronically infected promyelocytic leukaemia HL60 cells. The new HTLV-I isolate had an intact reading frame in the gag-pol region which could encode protein of 234 amino acids. This open reading frame has not been observed in previous HTLV-I isolates, although similar open reading frames have been reported in the corresponding locations in the related bovine leukaemia virus and HTLV type II. We consider that this open reading frame codes for the virus-encoded protease, on the basis of the homology of the predicted amino acid sequence with those of previously identified retrovirus proteases.