Three nucleoprotein components of alfalfa mosaic virus necessary for infectivity

Abstract

All five nucleoprotein components of alfalfa mosaic virus 425 have been purified by several cycles of density gradient centrifugation in a zonal rotor. The purified components were homogeneous in the analytical ultracentrifuge, had characteristic particle lengths, and were noninfectious at concentrations normally used for biological assay of the virus. Infectivity could be restored to usual values by combining three of the components provided that ethylenediamine tetraacetate was added during the purification procedure. These components were: bottom component, middle component, and top component b. None of these components could be omitted from the mixture without reducing the infectivity to very low values. On the other hand top components a and o were inactive in any combination whatsoever. Activity was not lost when one or two of the active components were exchanged with similar components from the virus isolates Caldy and 15 64 . These results together with those of earlier work strongly indicate that three components contribute unique and essential pieces of information to the genome of alfalfa mosaic virus. The fact that in earlier work with purified RNA species the middle component RNA was overlooked and that top component a RNA was thought to be active instead of top component b RNA is discussed.