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 i mmunodeficiency,virus structural proteins requires Rex and Rev protein s, respectively. Decreased expression of Gag and Env appears to be due , in part, to intragenic RNA sequences, termed cis-acting repressive s equences (CRS), and may be mediated by binding of specific cellular fa ctors. We demonstrated previously that two cellular proteins, p60CRS a nd p40CRS, interact,vith HTLV type 2 5' long terminal repeat CRS RNA a nd 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 radioimmunoprecipi tation of HeLa nuclear proteins UV cross-linked to CRS RNAs with murin e monoclonal antibodies, we now show that p40CRS is heterogeneous nucl ear ribonucleoprotein (hnRNP) Al and p60CRS is polypyrimidine tract-bi nding protein or hnRNP I. These immunoprecipitation results were confi rmed by an immunobinding assay with hnRNP I and hnRNP AI antibodies an d by cross-competition electrophoretic mobility shift experiments. In addition, we mapped a putative hnRNP Al binding site in U5 RNA and dem onstrated that p40CRS (hnRNP Al) binding to that site correlates with CRS function. Since both hnRNP I and hnRNP Al have been shown to influ ence splicing and potentially other steps in RNA processing, the bindi ng of both hnRNP I and hnRNP Al to HTLV RNA regulatory elements may al ter retrovirus RNA processing and may be involved in regulation by Rex .