Differences in electrophoretic behaviour of eight ribosomal proteins from rat and rabbit tissues and evidence for proteolytic action on liver proteins.

Divergence exists between eight ribosomal proteins of rat and rabbit. This is the first time such a divergence has been precisely demonstrated among mammals. In addition, a proteolytic activity, giving the appearance of modified proteins, is observed in the liver of both species but not in rabbit reticulocytes. These results were made possible by a recently developed method. Ribosomal proteins were compared by two-dimensional polyacrylamide gel electrophoresis in four different but related systems. The precise position of each individual protein was established in each of the four systems. Certain ribosomal proteins from different tissues, seemingly identical in one system were found to be different in other systems. Significant differences occurred between proteins of each ribosomal subunit from the two different species. Variation between reticulocyte and liver ribosomal proteins of the rabbit were minor. Several liver proteins of both species change position or disappear and apparently new proteins appear, if appropriate steps are not taken to prevent proteolysis. Differences in behavior of three small subunit and five large subunit proteins are attributable to an evolutionary divergence between the two species.