Characterization of acidic 60 S ribosomal proteins in Tetrahymena pyriformis

The ribosomes of eukaryotes contain acidic proteins that functionally [l-S] and antigenetically [3,6,7] are related to the Escherichia coli ribosomal proteins L7/L12. In contrast to their prokaryotic counterparts some of these eukaryotic acidic proteins are subject to phosphorylation in vivo [4,7-l 51. Generally, it appears that eukaryotic ribosomes contain two structurally related but distinct acidic proteins each of which may occur in phosphorylated forms [7,11,13,15]. The 60 S ribosomal subunit of Tetrahymena pyrzformis contains a triplet of acidic protein (L44-46) which according to electrophoretic properties, stainability and molecular weights resembles the putative L7/L12 equivalents of other eukaryotes [16]. However, our previous attempts to demonstrate phosphorylation in vivo of these T. pyrifomis ribosomal proteins have been uniformly negative [ 16,171. Since the L7/L12 equivalents of eukaryotic ribosomes, like their prokaryotic counterparts, seem to be intimately involved in at least elongation factor 1 and 2 dependent reactions [l-4], the possible complete lack of phosphorylation of these proteins in T. pytiformis was of interest both from a phylogenetic and a functional point of view. Here we present a more detailed analysis of the complement of acidic ribosomal proteins in T. pyriformis. The results indicate that the ribosomal proteins that electrophoretically resemble the putative L7/L12 equivalent of other eukaryotes are not phosphorylated in vivo.