The pX region of HTLV-I.

Gallo and his coworkers isolated a retrovirus (HTLV) from human cells derived from T-cell leukemia and lymphoma. Hinuma and his coworkers isolated independently a similar virus from a cell line derived from adult T-cell leukemia (ATL) patient. The occurrence of ATL correlates with the formation of antibody to ATL associated antigens or ATLA. To understand the etiological relationship between ATL and HTLV, we analyzed the antigens termed ATLA and found that they are polypeptides encoded by HTLV genome. We further studied the genome of HTLV and its gene expression in cells as well as in a cell-free translation system. We focused on a defective type HTLV produced from a cell line MT-2 that transforms normal lymphocytes most efficiently. The 24S defective gene of HTLV consists of a fused gene of gag-pXs and is amplified at the proviral state. The in vitro translation experiments revealed that the 24S defective gene of HTLV directs the synthesis of p28 of ATLA. By the sequence analysis of the amplified gag-pXs fused genes, we found that a carboxy terminal portion of p28 is translated from a pX-0 region. We further investigated a function of the gag-pX-0 fusion protein, p28. The p28 has an associated protein kinase activity that requires manganese instead of magnesium and phosphorylates the serine residue specifically. Another defective HTLV with a genomic 32S RNA was analyzed. The 32S defective genomic RNA forms a subgenomic 20S RNA in cells. The 20S mRNA is a transcript of an env-pXs fused genome and directs the synthesis of a fused glycoprotein, gp68 of ATLA. The sequence analysis of a cloned cDNA derived from the subgenomic 20S mRNA revealed that a coding frame of the entire pX-IV region is translated. In fact, an antibody against synthetic polypeptides of the pX-IV, immunoprecipitated the gp68. These results demonstrate at the first time that the pX-0 and pX-IV of HTLV genome are expressed in human cells. The biological activities of the fused pXs proteins are also discussed. Human T-cell leukemia virus type I (HTLV-I), a family of human retrovirus and the predicted causative agent of human adult T-cell leukemia/lymphoma (ATL) consists of the gag, pol, env, and pX regions (1).(ABSTRACT TRUNCATED AT 400 WORDS)