On the domain structure and the polymerization state of the Sendai virus Pprotein

The phosphoproteins (P) of paramyxoviruses and rhabdoviruses are cofactors of the viral polymerase (L) and chaperones of soluble nucleoprotein prevent ing its polymerization and nonspecific binding to cellular RNA. The primary sequences of six paramyxovirus P proteins were compared, and although ther e was virtually no sequence similarity, there were two regions with similar secondary structure predictions in the C-terminal part of P: the predicted multimerization domain and the X-protein, the sequence that binds to N in the N:RNA template. The C-terminal part of the Sendai virus P protein, the multimerization domain including the binding site for the polymerase, and t he X-protein were expressed in Escherichia coli All three polypeptides fold ed with secondary structures similar to those predicted. The C-terminal par t of P is a very elongated molecule with most of its length encompassing th e multimerization domain. Both the multimerization domain and the C-termina l part of P were found to form tetramers, whereas the X-protein was monomer ic. (C) 2000 Academic Press.