Long terminal repeat structure of an American isolate of type I human T-cell leukemia virus

Variation in the structure of the long terminal repeat (LTR) element of human T-cell leukemia virus (HTLV) types has been noted (M. Seiki, S. Hattori, Y. Hirayama, and M. Yoshida (1983), Proc. Natl. Acad. Sci. USA 80, 3618-3622; K. Shimotohno, D. W. Golde, M. Miwa, T. Sugimura, and I. S. Y. Chen (1984), Proc. Natl. Acad. Sci. USA 81, 1079-1083; J. Sodroski, M. Trus, D. Perkins, R. Patarca, F. Wong-Staal, E. Gelmann, R. Gallo, and W. Haseltine (1984), Proc. Natl. Acad. Sci. USA 81, 4617-4621). To determine whether HTLV isolates with similar disease associations, but from different geographic locations, exhibit a conserved LTR structure, the nucleotide sequence of the LTR of an American HTLV isolate from a patient with adult T-cell leukemia/lymphoma was obtained. Comparison of this LTR sequence to that of two Japanese HTLV isolates associated with a similar disease reveals a highly conserved organization of the U3, R, and U5 regions. The U. S. isolate differs from the Japanese viruses by only 15-16 bases out of 754 bases in the LTR region. These results show that Japanese HTLV isolates from patients with adult T-cell leukemia/lymphoma are members of the HTLV-I family and that LTRs of HTLV-I isolates are highly conserved. A 50-nucleotide imperfect direct repeat element is also identified in the U3 of the HTLV LTR distant from the cap site. The position and conserved nature of this sequence make it a likely candidate for a transcriptional enhancer.