Polypyrimidine tract-binding protein binds to the leader RNA of mouse hepatitis virus and serves as a regulator of viral transcription

A cellular protein, previously described as p55, binds specifically to the plus strand of the mouse hepatitis virus (MHV) leader RNA, We have purified this protein and determined by partial peptide sequencing that it is polyp yrimidine tract-binding protein (PTB) (also known as heterogeneous nuclear ribonucleoprotein [hnRNP] I), a nuclear protein which shuttles between the nucleus and cytoplasm, PTB plays a role in the regulation of alternative sp licing of pre-mRNAs in normal cells and translation of several viruses. By UV cross-linking and immunoprecipitation studies using cellular extracts an d a recombinant PTB, we have established that PTB binds to the MHV plus-str and leader RNA specifically. Deletion analyses of the leader RNA mapped the PTB-binding site to the UCUAA pentanucleotide repeats. Using a defective-i nterfering RNA reporter system, we have further shown that the PTB-binding site in the leader RNA is critical for MHV RNA synthesis, This and our prev ious study (H,-P. Li, X, Zhang, R Duncan, L, Comai, and M, M, C. Lai, Proc. Natl, Acad, Sci, USA 94:9544-9549, 1997) combined thus show that two cellu lar hnRNPs, PTB and hnRNP Al, bind to the transcription-regulatory sequence s of MHV RNA and may participate in its transcription.