Vim Research, 14 (1989) 175-188 Elsevier 175 VIRUS 00528 Budding efficiency of Sendai virus nucleocapsids: influence of size and ends of the RNA Genevieve Mottet and Laurent Roux Department of Microbiology, University of Geneva, Medical School, C. M. Il., Geneva, Switzerland (Accepted 13 July 1989) zyxwvutsrqponmlkjihgfedcbaZYXWVUT Summary The budding efficiency of Sendai virus antigenomes, as well as of defective interfering (DI) nucleocapsids of the deletion and copy-back types, was compared to that of the viral genome during infections of baby hamster kidney (BHK) cells. The antigenomes were shown to bud into virus particles as efficiently as the genomes, arguing for the irrelevance of the nucleocapsid-RNA ends in regulating the ef- ficiency of budding. The DI nucleocapsids, however, were restricted in their budding by factors inversely proportional to their size, arguing for an effect of nucleocapsid size in this process. This restriction in budding, however, appeared to be only expressed under conditions of very efficient DI-RNA replication. Sendai virus; Nucleocapsid; Budding Introduction Since the earliest description of defective interfering (DI) particles of influenza virus (von Magnus, 1954), all the negative-stranded RNA viruses have been shown to generate and amplify such particles. In general DI particles contain deleted genomes, which lack internal portions with conserved genomic 3’ and 5’ ends (deletion DI), or which lack the genomic 3’ end replaced by a copy of the 5’ end (copy-back DI; for a review see Holland et al., 1980; Perrault, 1981). When, in an effort to understand the mechanism of interference, DI particles containing nucleo- Correspondence ro: G. Mottet, Department of Microbiology, University of Geneva Medical School, C.M.U., 9 avenue de Champel, 1211 Geneva 4, Switzerland. 016%1702/89/$03.50 0 1989 Elsevier Science Publishers B.V. (Biomedical Division)