PROTEIN-INTERACTION DOMAINS OF THE MEASLES-VIRUS NUCLEOCAPSID PROTEIN(NP)

The currently accepted model for measles virus (MV) transcription and replication assumes the nucleocapsid (NP) protein to possess the abili ty to bind to RNA, to other NP molecules, and to the phosphoprotein (P ) during ribonucleocapsid (RNP) assembly, as well as to the matrix pro tein (M) during virion assembly. We have cloned the MV NP open reading frame and have expressed the protein in bacteria as a fusion with glu tathione-S-transferase (GST). Affinity purified GST-NP fusion protein has been used as a probe to examine the interaction of NP with [S-35] methionine labeled proteins from MV-infected cells. We have demonstrat ed definite and specific interactions between NP and itself and betwee n NP and P, but have been unable to demonstrate any interaction betwee n NP and M. We have been able to provide independent confirmation of t his pattern of interaction using the yeast two-hybrid assay. We have, in addition, been able to map the domains of NP involved in these inte ractions by assays using sets of amino- and carboxy-terminal deletion mutants of GST-NP. The NP-NP interaction domain was found to reside in the highly conserved middle and amino-terminal domains of the protein . The hyper-variable carboxy-terminus and the conserved middle domain appear to constitute separate and independent sites for the binding of P to NP. The significance of these findings in regard to MV transcrip tion and replication is discussed.