Association of Proteins with the Stress 70 Molecular Chaperones at Low Temperature: Evidence for the Existence of Cold Labile Proteins in Spinach

Molecular chaperones of the stress 70 family reversibly bind and release nonnative proteins in a nucleotide-dependent cycle. Purified monoclonal antibodies prepared against spinach (Spinacia oleracea) stress 70 molecular chaperones were used in immunoprecipitation experiments with extracts of spinach leaf tissue pulse-labeled with [³⁵S]methionine in an effort to detect whether low-temperature exposure altered the biogenesis or the native state stability of any proteins leading to the formation of complexes with the stress 70 molecular chaperones. The two monoclonal antibodies used in this research are highly specific for the cytosolic or ER-luminal stress 70 molecular chaperones. Analyses of the immunoprecipitation results indicate that low temperature causes an increased association of some proteins with the two chaperones. The findings are consistent with the hypothesis that normal biogenesis or the conformational stability of specific proteins may be unfavorably altered at low temperature in spinach and perhaps other plants.