Coronavirus nucleocapsid protein. RNA interactions.

The coronavirus nucleocapsid protein (N) is involved in encapsidation and packaging of viral RNA. In this study we investigated the ability of the bovine coronavirus (BCV) N protein to interact with RNA. Histidine-tagged BCV N (his-N) protein was expressed in bacteria. A filter binding assay was established to quantitatively measure the binding efficiency of purified his-N to different RNAs. The results indicate that bacterially expressed N bound both BCV and mouse hepatitis coronavirus (MHV) RNAs. Binding to in vitro generated BCV and MHV RNA transcripts was significantly higher than binding to a non-coronavirus RNA. Similar binding efficiencies were measured for a BCV defective genome, pDrep, and a transcript that contained the MHV packaging signal. Interestingly, the entire MHV DI, pMIDI-C, was bound at a higher efficiency than the packaging signal alone. This is one of the first reports to show that N interacts with the MHV packaging signal.