CHARACTERIZATION OF RIBOSOMAL-PROTEIN PHOSPHORYLATION IN MAIZE AXES DURING GERMINATION

Ribosomal proteins from maize (Zea mays L.) axes were in vivo P-32-lab eled at different germinating periods. These proteins were analyzed by 1- and 2-D gel electrophoresis and autoradiography. Specific P-32-rib osomal protein patterns were found within the 24 h tested period. The main labeled bands corresponded to 37, 31, 16 and 14.5 kDa. The 31 kDa labeled band appeared on the labeled pattern from 8 h incubation onwa rd, while P-32-incorporation on the 16 and 14.5 kDa bands decreased al ong the germination period. Early phosphorylation of the 31 kDa protei n was achieved by stress (heat or anoxia shock) but not by phytohormon es. Hydrolysis of the phosphoproteins and paper electrophoretic analys is of the amino acids showed phosphoserine threonine as the labeled re sidues. Separation of the ribosomal subunits and analysis of the corre spondent proteins indicated that the 31 kDa phosphoprotein is located in the small subunit, while the 14.5, 16 and 37 kDa phosphoproteins ar e part of the large subunit. Furthermore, the 31 kDa protein appeared labeled in the 2-D gel autoradiography and showed cross reaction with antibodies raised vs. rat S6 ribosomal protein by immunoprecipitation. Acidic ribosomal proteins were extracted from the total ribosomal pro teins and analyzed by gel electrophoresis and autoradiography. Results indicated that the extracted proteins corresponded to the 37, 16 and 14.5 kDa phosphoproteins. These proteins gave positive reaction in slo t blot analysis using antibodies raised vs. the correspondent yeast ac idic ribosomal proteins. The possible significance of the phosphorylat ion of these proteins in regulating protein synthesis during seed germ ination is discussed.