Expression of the structural proteins of human immunodeficiency virus type (HIV-1) requires the Rev protein encoded by the rev open reading frame. Rev protein interacts with Rev-responsive element RRE located in the env region of the viral mRNA and seems to mediate the export of the incompletely spliced viral mRNA to the cytoplasm. RRE has a complex secondary structure which is composed of a central stem (I`), a small stem (I) and 5 stem/loops (II, III, IV, V, VI). To investigate which region of RRE is essential for the interaction with Rev protein, mutational analysis in RRE was carried out. We examined the nature of the mutated RRE in several assay systems, p24 ELISA assay, Reverse Transcriptase assay and CAT assay. Here we show that the secondary structure of stem/loop II region is critical for Rev response. Other structural components within RRE RNA seem to have only subsidiary roles. We also show that RRE appears to contain a negative sequence which hinders the expression of structural gene in the absence of the Rev protein.