Expression of the pX gene of HTLV-I: general splicing mechanism in the HTLV family.

Human T-cell leukemia virus type I (HTLV-I) is an etiological agent of adult T-cell leukemia. A viral gene pX encodes for p40X and it has been proposed that this protein trans-activates the viral long terminal repeat and possibly some cellular genes; this activation may be associated with T-cell transformation. The mechanism of pX gene expression and the primary structure of p40X are now reported. Two-step splicing generates the 2.1-kilobase pX mRNA; the initiator methionine for env becomes part of the pX protein. These splicing signals are conserved among all members of the HTLV family except for the acquired immune deficiency syndrome-associated viruses.