CHARACTERIZATION AND PHYSIOLOGICAL-FUNCTION OF CLASS-I LOW-MOLECULAR-MASS, HEAT-SHOCK PROTEIN COMPLEX IN SOYBEAN

Examination of an ammonium sulfate-enriched fraction (70-100% saturati on) of heat-shock proteins (HSPs) by nondenaturing polyacrylamide gel electrophoresis revealed the presence of a high molecular mass complex (280 kD) in soybean (Glycine max) seedlings. This complex cross-react ed with antibodies raised against soybean class I low-molecular-mass ( LMW) HSPs. Dissociation of the complex by denaturing polyacrylamide ge l electrophoresis showed the complex to contain at least 15 polypeptid es of the 15- to 18-kD class I LMW HSPs that could be detected by stai ning, radiolabeling, and western blotting. A similar LMW-HSP complex w as observed in mung bean (Vigna radiata L.; 295 kD), in pea (Pisum sat ivum L.; 270 kD), and in rice (Oryza sativa L.; 310 kD). The complex w as stable under high salt conditions (250 mM KCl), and the integrity w as not affected by 1% Nonidet P-40 and 3 mu g/mL RNase treatment. The size of the isolated HSP complex in vitro was conserved to 55 degrees C; however, starting at 37.5 degrees C, it changed to higher molecular forms in the presence of soluble proteins. The isolated HSP complex w as able to protect up to 75% of the soluble proteins from heat denatur ation in vitro.