Measles virus nucleocapsid protein can function in Sendai virus defective interfering particle genome synthesis in vitro.
The Sendai virus P and L proteins, the viral RNA polymerase, and the nucleocapsid protein, NP, synthesized in a transient mammalian expression system support the replication of Sendai virus defective interfering particle (DI) genome RNA in vitro. We have shown that the measles virus nucleocapsid protein, N, can substitute for the Sendai NP protein in genome synthesis. The chimeric product nucleocapsids, which contained Sendai RNA encapsidated with measles N protein, were atypical since they were sensitive to micrococcal nuclease digestion, unlike wild-type Sendai or measles nucleocapsids. The utilization of measles N protein required the endogenous Sendai virus RNA polymerase, since DI nucleocapsids free of polymerase were not replicated. Although both Sendai virus NP and P proteins and measles N and P proteins formed complexes when they were coexpressed, sedimentation analysis showed that measles N protein self-assembled and did not form a complex when expressed with the Sendai P protein. Furthermore, when the Sendai P-L polymerase complex was provided separately, measles N protein alone synthesized DI genome RNA in the absence of Sendai P protein. These data suggest that the self-assembled form of measles N protein functions in Sendai DI genome synthesis.