The RNA interacting domain but not the protein interacting domain is highly conserved in ribosomal protein P0

Protein P0 interacts with proteins P1 alpha, P1 beta, P2 alpha, and P2 beta , and forms the Saccharomyces cerevisiae ribosomal stalk. The capacity of R PP0 genes from Aspergillus fumigatus, Dictyostelium discoideum, Rattus norv egicus, Homo sapiens, and Leishmania infantum to complement the absence of the homologous gene has been tested. In S. cerevisiae W303dGP0, a strain co ntaining standard amounts of the four P1/P2 protein types, all heterologous genes were functional except the one from L. infantum, some of them induci ng an osmosensitive phenotype at 37 degrees C. The polymerizing activity an d the elongation factor-dependent functions but not the peptide bond format ion capacity is affected in the heterologous P0 containing ribosomes. The h eterologous P0 proteins bind to the yeast ribosomes but the composition of the ribosomal stalk is altered. Only proteins P1 alpha and P2 beta are foun d in ribosomes carrying the A. fumigatus, R. norvegicus, and H. sapiens pro teins. When the heterologous genes are expressed in a conditional null-P0 m utant whose ribosomes are totally deprived of P1/P2 proteins, none of the h eterologous P0 proteins complemented the conditional phenotype. In contrast , chimeric P0 proteins made of different amino-terminal fragments from mamm alian origin and the complementary carboxyl-terminal fragments from yeast a llow W303dGP0 and D67dGP0 growth at restrictive conditions, These results i ndicate that while the P0 protein RNA-binding domain is functionally conser ved in eukaryotes, the regions involved in protein-protein interactions wit h either the other stalk proteins or the elongation factors have notably ev olved.