Identification and characterization of an extended Tax protein in human T-cell lymphotropic virus type II subtype b isolates.

The tax gene sequence of human T-cell lymphotropic virus type II isolate G12 (HTLV-IIG12) was found to encode an extended Tax protein when compared with that of HTLV-IIMoT. In vitro transcription-translation of the HTLV-IIG12 tax gene produced a 40-kDa Tax protein that specifically reacted with serum specimens from HTLV-II-infected individuals. Limited sequence analysis demonstrated that isolates with an extended Tax protein were all HTLV-II subtype b (HTLV-IIb). Therefore, the extended Tax protein appears to be a unique characteristic of most HTLV-IIb isolates and may be useful in designing immunoassays to distinguish between HTLV-IIa and HTLV-IIb.