Functional mapping of the activity of the R region in the human T-cell leukemia virus type I long terminal repeat to increase gene expression.

We previously demonstrated the activity of the R fragment in the long terminal repeat of human T-cell leukemia virus type I for elevation of the level of gene expression. In this study, the fragment was deleted with BAL31 nuclease to determine its functional domain. Series of the shortened R fragments were linked to the simian virus 40 promoter unit, which regulated expression of a reporter gene. Examination with the R fragments deleted from the 5' and 3' ends showed that borders of the functional domain were mapped within nucleotide positions 458 to 473 for the 5' end and nucleotide positions 559 to 594 for the 3' end, respectively. Thus we conclude that a 136-base-pair fragment corresponding to the second half of the R region was sufficient to allow elevation of the level of gene expression.