Abstract
Concanavalin A (Con. A), a phytagglutinin derived from Canavalia ensiformis, binds specifically to several branched carbohydrates (Goldstein, Hollerman & Merrick, 1965), containing terminal non-reducing α-D-glucopyranosyl, α-D-mannopyranosyl or -D-fructofuranosyl residues (Goldstein, Hollerman & Smith, 1965; Goldstein & So, 1965).
Recently Bernhard & Avrameas (1971) developed a method to visualize the reaction of a cell surface with Con. A with the electron microscope. This gave us the opportunity to use Con. A to study the structure of the envelope of two RNA tumour viruses that mature at the cell membrane. B particles of the mouse mammary tumour virus (MTV-s) and C particles of a murine leukaemia virus (Rauscher) were used for this purpose.
The similarity of the Con. A-polysaccharide interaction to antibody-antigen precipitation is striking (So & Goldstein, 1967). We therefore tried to observe directly the interaction between the virus particles and Con. A after negative staining with phosphotungstic acid (PTA), as has been done with the virus-antibody complexes (Lafferty & Oertelis, 1963).