Ribosomal Proteins from Rabbit Reticulocytes: Numbers, Molecular Weights, Relative Amounts and Phosphorylation by Protein Kinases

Abstract

The ribosomal proteins from the 40S and 60S subunits of rabbit reticulocyte ribosomes have been analyzed by 2-dimensional polyacrylamide gel electrophoresis and by gel electrophoresis in sodium dodecyl sulfate. Seventy-one proteins, 32 in the 40S subunit and 39 in the 60S subunit, were identified. Molecular weights for each protein were determined. Analysis of this data suggests that the ribosomal particles are homogeneous in protein composition. Four protein kinase activities were purified from the supernatant fraction. Three of these had similar substrate specificity with respect to histone, casein and ribosomal proteins. A fourth enzyme, specific for casein, was shown to phosphorylate different ribosomal proteins than the other three enzymes. The protein bands serving as substrates for the protein kinases were identified by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. Two proteins from the 40S subunit and nine from the 60S subunit were substrates for the protein kinases.

Supported by grants from the American Heart Association (72–867) and the Damon Runyon Memorial Fund (DRG-1140).