Changes in Morphology, Infectivity and Haemagglutinating Activity of Semliki Forest Virus Produced by the Treatment with Caseinase C from Streptomyces albus G.

Abstract

SUMMARY: Electron micrographs of negatively stained Semliki Forest virus were made before and after treatment of the virus with caseinase C from Streptomyces albus G. The virus appeared as roughly spherical (diameter 550–590 Å), covered with projections and sometimes bearing an appendix, which seemed to be a fold of the envelope. Treated with caseinase C in tris buffered saline, the virus lost its projections and its haemagglutinating activity but remained infectious. The site of haemagglutination, then, is probably located on the projections. Treated with caseinase C in phosphate buffer, the virus lost its infectivity as well as its haemagglutinating activity; the number of the remaining viral particles was not significantly modified. These structures had no projections; their envelope was degraded and sometimes completely destroyed. In this case, they had a smaller diameter (385–390 Å) than the projectionless particles obtained by treatment in tris buffered saline (410–460 Å). As the virus particles with degraded envelope still contained as much infectious RNA as the controls, it was thought that some degree of integrity of the envelope was necessary for the particle infectivity. Thus the site for infectivity appeared to be different from that for haemagglutination.