CYTOPLASMIC DOMAIN OF SENDAI VIRUS HN PROTEIN CONTAINS A SPECIFIC SEQUENCE REQUIRED FOR ITS INCORPORATION INTO VIRIONS

In the assembly of paramyxoviruses, interactions between viral protein s are presumed to be specific. The focus of this study is to elucidate the protein-protein interactions during the final stage of viral asse mbly that result in the incorporation of the viral envelope proteins i nto virions. To this end, we examined the specificity of HN incorporat ion into progeny virions by transiently transfecting HN cDNA genes int o Sendai virus (SV)infected cells. SV HN expressed from cDNA was effic iently incorporated into progeny Sendai virions, whereas Newcastle dis ease virus (NDV) HN was not. This observation supports the theory of a selective mechanism for HN incorporation. To identify the region on H N responsible for the selective incorporation, we constructed chimeric SV and NDV HN cDNAs and evaluated the incorporation of expressed prot eins into progeny virions. Chimera HN that contained the SV cytoplasmi c domain fused to the transmembrane and external domains of the NDV HN was incorporated to SV particles, indicating that amino acids in the cytoplasmic domain are responsible for the observed specificity. Addit ional experiments using the chimeric HNs showed that 14 N-terminal ami no acids are sufficient for the specificity. Further analysis identifi ed five consecutive amino acids (residues 10 to 14) that were required for the specific incorporation of HN into SV. These residues are cons erved among all strains of SV as well as those of its counterpart, hum an parainfluenza virus type 1. These results suggest that this region near the N terminus of HN interacts with another viral protein(s) to l ead to the specific incorporation of HN into progeny virions.