Preparation of soluble, biologically active alfalfa mosaic virus coat protein and its CaCl2-induced degradation.

A method for the preparation of soluble protein from five biologically distinct alfalfa mosaic virus (AMV) isolates is described. Highly purified AMV was dissociated with 1 M CaCl2 in 10 mM sodium acetate, pH 6.0, and the precipitated RNA was removed by centrifugation. The protein was dialysed against 10 mM sodium acetate, pH 6.0, containing 0.1 M CaCl2. If the salt concentration was reduced further, proteins from some AMV isolates precipitated. Proteins prepared by this method were shown to be immunoreactive and to activate the infectivity of the AMV genome. However, during prolonged exposure of the protein to buffers containing 0.1 M CaCl2, it undergoes slow proteolysis thereby losing its ability to activate the AMV genome but not its immunoreactivity.