Functional conversion from HIV-1 Rev to HTLV-1 Rex by mutation

Modulation of HTLV-I gene expression by HIV-1 Rev through an alternative RxRE-independent pathway mediated by the RU5 portion of the 5'-LTR

The 5'-RU5 portion of human T-lymphocyte virus type I (HTLV-I) long terminal repeat (LTR) had been reported to contain cis-acting elements for the controlled viral gene expression by the rex gene product. In this study, the human immunodeficiency virus type I (HIV-1) Rev protein was found to enhance gene expression, acting through the 5'-RU5 portion of HTLV-I, while the Rex-responsive element (RxRE)-mediated activation by Rev was reconfirmed to be negative. This positive action of HIV-1 Rev on HTLV-I gene expression seemed to be distinct from the widely accepted Rex or Rev function to facilitate the nuclear export of RxRE-containing unspliced viral mRNAs, since a trans-dominant, nuclear export-deficient mutant (RevM10) still retained the RU5-mediated effector function. Analyses of the functional aspects of Tat/Rev fusion proteins on the HTLV-I RU5 suggested a specific interaction of Rev and RU5, but lacked evidence for the binding of Rev to the RU5 at the RNA level. These results suggest an answer to the controversy regarding a Rex-like function occasionally observed with HIV-1 Rev and its related proteins. It may also be suggested that particular care should be taken when such a trans-dominant Rev mutant is considered to be used as a genetic therapy against HIV-I infection, in individuals infected with both HIV-I and HTLV-1.

Inhibition of human immunodeficiency virus type 1 Rev function by a Rev mutant which interferes with nuclear/nucleolar localization of Rev

A nonfunctional mutant of human immunodeficiency virus type 1 Rev was created by deleting seven amino acid residues within the nucleolar targeting signal. This mutant Rev remained in the cytoplasm in expressed cells and strongly inhibited the function of Rev by interfering with the nuclear/nucleolar localization of coexpressed Rev. These findings strongly suggest the multimerization of Rev in the cytoplasm before migration to the nucleus/nucleolus, where wild-type Rev functions as a trans-regulator.