COMPARATIVE-STUDY BETWEEN PROKARYOTES AND EUKARYOTES BY CHEMICAL IODINATION OF RIBOSOMAL-PROTEINS

Escherichia coli and Saccharomyces cerevisiae ribosomal proteins were chemically iodinated with 125I by chloramine T under conditions in which the proteins were denatured. The labeled proteins were subsequently separated by 2-dimensional gel electrophoresis with an excess of untreated ribosomal proteins from the same species. The iodination did not change the electrophoretic mobility of the proteins as shown by the pattern of spots in the stained gel slabs and their autoradiography. The 125I radioactivity incorporated in the proteins was estimated by cutting out the gel spots from the 2-dimensional electrophoresis gel slabs. The highest content of 125I was found in the ribosomal proteins L2, L11, L13, L20/S12, S4 and S9 from E. coli, and L2/L3, L4/L6/S7, L5, L19/L20, L22/S17, L29/S27, L35/L37 and S14/S15 from S. cerevisiae. Comparisons between the electrophoretic patterns of E. coli and S. cerevisiae ribosomal proteins were carried out by coelectrophoresis of labeled and unlabeled proteins from both species. E. coli ribosomal proteins L5, L11, L20, S2, S3 and S15/S16 overlapped with L15, L11/L16, L36/L37, S3, S10 and S33 from S. cerevisiae, respectively. Similar coelectrophoresis of E. coli 125I-labeled proteins with unlabeled rat liver and wheat germ ribosomal proteins showed that the former overlap with proteins L1, L11, L14, L16, L19, L20 and the latter with L2, L5, L6, L15, L17 from E. coli.