SPECIFIC BINDING OF POLYPYRIMIDINE TRACT BINDING-PROTEIN AND HNRNP A1TO HIV-1 CRS ELEMENTS

The human immunodeficiency virus (HIV) Rev and human T-cell leukemia v irus (HTLV) Rex proteins regulate viral RNA processing. Both proteins act to overcome the block to viral structural gene expression, at leas t in part, by reversing the inhibitory effect of intronic RNA sequence s, termed cia-acting repressive (CRS) sequences. Using HTLV type II (H TLV-II) as a model, we recently showed that the function of a 5' long terminal repeat (LTR) CRS correlates with in vitro binding by both pol ypyrimidine tract binding (PTB) protein (also known as hnRNP I) and hn RNP A1 to CRS RNA (1,2). Using radioimmunoprecipitation of proteins ul traviolet (UV) crosslinked to each HIV CRS RNA with monoclonal anti-hn RNP antibodies, we now demonstrate that hnRNP I and hnRNP A1 bind to t wo different HIV-1 CRS RNAs. In addition, we show that hnRNP I and hnR NP A1 binding to HIV-1 CRS RNAs can be specifically competed by HTLV-I I CRS RNAs using electrophoretic mobility shift assay (EMSA)/UV crossl inking assays. Binding by both hnRNP I and hnRNP A1 to HIV-1 and HTLV- II CRS RNAs suggests a role for these proteins in CRS function that ma y be influenced by the Rev and Rex proteins, respectively.