Degradation of Bowman-Birk protease inhibitor mRNA with a cell-free extract.

A cell-free mRNA degradation system consisting of the polysomal and postpolysomal fractions was obtained from cultured soybean cotyledons for studying Bowman-Birk protease inhibitor (BBPI) mRNA stability. This in vitro system reflected the shorter in vivo half-life of BBPI mRNA of cotyledons cultured in basal-medium as compared to cotyledons cultured in methionine-supplemented medium. Most of the BBPI mRNA degradative activity was found to be present in the postpolysomal supernatant fraction. The higher rate of BBPI mRNA degradation in basal medium-cultured cotyledons was due to an increased destabilizing activity specific to BBPI mRNA in the postpolysomal fraction from basal-medium cultured cotyledons. The specificity was absent when purified RNA was used as the substrate. Degradation of the mRNA was not divalent cation-dependent and was inhibited in the presence of higher concentrations of monovalent and divalent cations.