THE HYPERVARIABLE C-TERMINAL TAIL OF THE SENDAI PARAMYXOVIRUS NUCLEOCAPSID PROTEIN IS REQUIRED FOR TEMPLATE FUNCTION BUT NOT FOR RNA ENCAPSIDATION

The paramyxovirus nucleocapsid proteins (NPs) are relatively well cons erved, except for the C-terminal 20% (or ca. 100 amino acids), referre d to as the tail. We have examined whether this hypervariable tail is required for genome synthesis, both in vitro, where synthesis is predo minantly from the input templates, and in vivo, where multiple rounds of amplification occur. In these viruses, genome synthesis and assembl y of the nascent chain are coupled. We find that the tail is required in vivo but not in vitro. Closer examination of the in vivo system sho wed that the tailless NP could encapsidate the genome chain but that a mplification did not occur. We interpret these results as indicating t hat the tail is not required for RNA assembly but is required for the template to function in RNA synthesis. Relatively small deletions with in the conserved N-terminal 80% of the protein, on the other hand, ren dered the protein nonfunctional in either system. The possible functio ns of the tail in RNA synthesis are discussed.