PURIFICATION AND PROPERTIES OF ARABIDOPSIS-THALIANA COR (COLD-REGULATED) GENE POLYPEPTIDES COR15AM AND COR6.6 EXPRESSED IN ESCHERICHIA-COLI

Arabidopsis thaliana cold-regulated genes COR15a and COR6.6 encode 15- and 6.6-kD polypeptides, respectively. The COR15a polypeptide is know n to be targeted to chloroplasts and, during import, to be processed t o a 9.4-kD polypeptide designated COR15am. The COR6.6 polypeptide is t hought to be located in the cytosol. The coding sequences for COR15am and COR6.6 were fused to the bacteriophage T7 promoter and expressed i n Escherichia coli. The recombinant polypeptides COR15am(r) and COR6.6 (r) were purified to near homogeneity using a combination of ammonium sulfate fractionation, ion-exchange chromatography, and adsorption chr omatography on hydroxyapatite. COR15am(r) and the major species of COR 15am in chloroplasts co-migrated on both two-dimensional O'Farrell gel s and nondenaturing polyacrylamide gels. These data corroborate the si te of COR15a processing and indicate no difference in charge or quater nary structure between COR15am(r) and the major species of COR15am in plants. In contrast, the migration patterns of COR6.6(r) and COR6.6 on two-dimensional gels suggest that a considerable portion of the COR6. 6 population in plants is modified. In the accompanying papers (M.S. W ebb, S.J. Gilmour, M.F. Thomashow, P.L. Steponkus [1996] Plant Physiol ogy 111: 301-312; M. Uemura, S.J. Gilmour, M.F. Thomashow, P.L. Stepon kus [1996] Plant Physiology 111:313-327), the effects of COR15am(r) an d COR6.6(r) on the cryostability and lyotropic phase behavior of lipos omes are examined.