AN N-TERMINAL DOMAIN OF THE SENDAI PARAMYXOVIRUS P-PROTEIN ACTS AS A CHAPERONE FOR THE NP PROTEIN DURING THE NASCENT CHAIN ASSEMBLY STEP OFGENOME REPLICATION

Two domains involved in RNA synthesis have recently been found within the N-terminal 77 amino acids of the Sendai virus P protein. One domai n is required for RNA synthesis per se and has properties in common wi th the transactivation domains of cellular transcription factors. The second domain is thought to be specifically required for the nascent c hain assembly step in genome replication. We have further mapped this second domain by the construction of chimeric and deleted P proteins t o amino acids 33 to 41 of P and by examining the abilities of these P proteins to support DI genome replication in vivo Using glycerol gradi ent sedimentation, we have shown that this domain is required to form a stable complex with unassembled NP (P-NP0) and to prevent NP from as sembling illegitimately, i.e., independently of the concurrent assembl y of a nascent viral genome. Since the P-NP0 complex represents the fu nctional form of unassembled NP which is delivered to the nascent chai n during genome replication, and since amino acids 33 to 41 are not re quired for the stable interaction of P with the assembled NP of the nu cleocapsid, this chaperone function of P is not required for mRNA synt hesis or the RNA synthesis step of genome replication.