Purified reovirus type 3 (strain Dearing) was treated with monoclonal anti-?l
antibody conjugated to ferritin and examined in the electron microscope. Virion associated
ferritin molecules corresponding to locations of the ?l protein were
observed. Electron microsocpy of thin sections of these preparations revealed that
ferritin conjugates were localized at the vertices of the viral icosahedron. Reovirus
cores possessing spikes and protein ?1, prepared by partial chymotrypsin digestion
of intact virions, were similarly treated and examined. Core-associated ferritin
molecules were found to be localized at positions corresponding to the tips of the
spikes. Such an association was not observed with the cores whose spikes had been
removed by alkali treatment. These results provide unequivocal evidence that protein
ol is present in icosahedrally-distributed locations, representing tips of reovirus core
spikes, on the surface of reovirus particles