HIV-1 Rev protein plays an important role in regulating the expression of viral structural proteins. It allows the nuclear export and accumulation of unspliced and partially spliced viral mRNA in the cytoplasm. The Rev-responsive element RNA, present in the env gene, forms a higly ordered RNA secondary structure and is required for the Rev-mediated mRNA export. For this process to complete factor(s) are strongly suggested. From our experiments of electrophoretic mobility shift, UV-crosslinking and SDS/PAGE, RRE RNA was found to be recognized to several nuclear factors such as 36/37, 56, 41. 76, 150 kD proteins in the order of reactivity. Among them, 36/37 and 56 kD proteins are more reactive upon a brief UV treatment (5 min) and more persistent in the presence of high amount of nonspecific competitor, heparin. Certain nuclear protein9s) seemed to recognize the RRE RNA structure in competition with Rev to gel mobility shift assay.