Heterogenetic, interspecific nature of ribosomal proteins in mammals

Abstract

The nature of the differences between ribosomal proteins of mammalian species (man, mouse, rat, hamster), separated by polyacrylamide gel electrophoresis, has been investigated in cell lines and inter‐specific somatic hybrids cultured in vitro, and in livers of the corresponding animals. The proteins of the large and small ribosomal subunits have only a few bands with the same electrophoretic mobilities. Comparing, for each kind of subunit, the ribosomal proteins in the four species, two categories of proteins are described: (a) proteins which are always present, qualitatively and quantitatively constant; (b) proteins which exhibit qualitative or quantitative differences. One qualitative difference, possibly due to a mutation slightly altering the electrophoretic mobility of one protein of the large subunit of the syrian hamster has been observed. The mouse‐hamster hybrid cells possess on their large ribosomal subunits, the proteins from each “parent”. Several quantitative differences, affecting only certain proteins of the subunits, are described. They seem to be the main source of the heterogeneity of ribosomal proteins observed between mammalian species. These findings are discussed in relation to the expression of the genome, and to the structure and function of the ribosomes during the process of speciation and differentiation.