LOCALIZATION OF THE RNA-BINDING DOMAIN OF MOUSE HEPATITIS-VIRUS NUCLEOCAPSID PROTEIN

The 454-amino acid nucleocapsid (N) protein of mouse hepatitis virus ( MHV) binds the leader RNA sequence located at the 5' ends of all plus- sense genomic and subgenomic viral mRNAs. Purified N protein was cleav ed with formic acid to determine which domain interacts with the leade r RNA sequence. Incubation at 42-degrees-C resulted in partial cleavag e into two fragments of M(r)s of approximately 32K and 37K and three f ragments of 17K, 16K and 14K. Incubation at 56-degrees-C resulted in c omplete cleavage yielding only the three lower molecular mass products . Both the 32K and 37K partial cleavage products and one of the comple te cleavage products bind MHV leader RNA, suggesting that the central region of the N protein contains the RNA-binding domain. Monoclonal an tibody mapping of the cleavage products confirmed that the MHV leader RNA binding domain is contained within the central 140-amino acid frag ment, comprising amino acids 169 to 308. Analysis of the amino acids w ithin this domain indicates no similarity to any previously described RNA-binding protein. suggesting that N protein may possess a unique RN A-binding motif.