Preferred nucleotide sequence at the integration target site of human T-cell leukemia virus type I from patients with adult T-cell leukemia

Human T-cell leukemia virus type I (HTLV-I) is etiologically associated with adult T-cell leukemia/lymphoma (ATL). We cloned and sequenced host DNA adjacent to the long terminal repeats of HTLV-I from uncultured leukemic cells of 4 ATL patients. The region flanking the provirus was generally A/T-rich (60-64% A/T), and a nucleotide composition bias was noticed when sequences within 25 bp on both sides of the integration target site were analyzed. In the 6-bp direct repeat, both end positions are preferentially occupied by G/C, whereas the middle positions are preferentially occupied by A/T. Furthermore, AA or TT dinucleotides are frequently present on each side adjacent to the center of the direct repeat. Our finding suggests preferential integration target sites of HTLV-I in the host genome. Further study is warranted to determine whether each of the target sequence preference is a general property of HTLV-I integration or may be associated with the leukemogenesis of ATL.