POLYPYRIMIDINE TRACT-BINDING PROTEIN AND HETEROGENEOUS NUCLEAR RIBONUCLEOPROTEIN A1 BIND TO HUMAN T-CELL LEUKEMIA-VIRUS TYPE-2 RNA REGULATORY ELEMENTS

Efficient expression of human T-cell leukemia virus (HTLV) and human immunodeficiency,virus structural proteins requires Rex and Rev proteins, respectively. Decreased expression of Gag and Env appears to be due, in part, to intragenic RNA sequences, termed cis-acting repressive sequences (CRS), and may be mediated by binding of specific cellular factors. We demonstrated previously that two cellular proteins, p60CRS and p40CRS, interact,vith HTLV type 2 5' long terminal repeat CRS RNA and that the interaction of both proteins with CRS RNA correlates with function (A. C. Black, C. T. Ruland, J. Luo, A. Bakker, J. K. Fraser, and J. D. Rosenblatt, Virology 200:29-41, 1994). By radioimmunoprecipitation of HeLa nuclear proteins UV cross-linked to CRS RNAs with murine monoclonal antibodies, we now show that p40CRS is heterogeneous nuclear ribonucleoprotein (hnRNP) Al and p60CRS is polypyrimidine tract-binding protein or hnRNP I. These immunoprecipitation results were confirmed by an immunobinding assay with hnRNP I and hnRNP AI antibodies and by cross-competition electrophoretic mobility shift experiments. In addition, we mapped a putative hnRNP Al binding site in U5 RNA and demonstrated that p40CRS (hnRNP Al) binding to that site correlates with CRS function. Since both hnRNP I and hnRNP Al have been shown to influence splicing and potentially other steps in RNA processing, the binding of both hnRNP I and hnRNP Al to HTLV RNA regulatory elements may alter retrovirus RNA processing and may be involved in regulation by Rex.