A small element from the Mason-Pfizer monkey virus genome makes human immunodeficiency virus type 1 expression and replication Rev-independent.

Replication of human immunodeficiency virus type 1 (HIV-1) is dependent on the viral Rev protein. This protein acts in concert with the cis-acting rev-responsive element present in intron-containing RNAs to facilitate nuclear export of these RNAs. Here we show that a cis-acting 219-nucleotide sequence from an unrelated "simple" retrovirus, Mason-Pfizer monkey virus (MPMV), enables Rev-independent HIV-1 replication. This sequence is present in an untranslated region near the 3' end of the MPMV genome. The MPMV element is also able to efficiently substitute for Rev in expression of Gag/Pol and Env proteins from subgenomic constructs. We hypothesize that the MPMV element functions by interacting with a cellular factor that plays a role in mRNA transport analogous to that of the Rev protein. It might be possible to exploit this element in the development of an HIV vaccine.