Molecular cloning of the gene encoding an acidic ribosomal protein of the P2 family from the ciliate Euplotes raikovi

We have characterized a macronuclear gene of the ciliate protozoan Euplotes raikovi, which encodes an acidic ribosomal protein of the P protein family . This gene shows the typical organization of the hypotrich ciliate macronu clear "gene-sized" molecules with Euplotes telomeres at the ends. The longe st open reading frame encodes a conceptual protein of 113 amino acid residu es, with a molecular mass and pi value of 11.45 kDa and 3.97, respectively. By using sequence homology analysis, the protein was found to belong to th e ribosomal P2 protein family and was named Er P2, where Er stands for Eupl otes raikovi. These proteins, generally called A (acidic/alanine rich) prot eins in prokaryotes and P (phosphorylated) proteins in eukaryotes, in which they are divided into P1 and P2 families, play a role in the elongation st ep of protein synthesis. Approximately 40% amino acid sequence identity was found between the cloned protein and other known protozoan ribosomal P2 pr oteins. Within its N-terminal half, this protein contains several potential kinase phosphorylation sites. Protein Er P2 differs markedly from the cons ensus P protein sequence in its C-terminal region, usually highly conserved among eukaryotic ribosomal P proteins, and shows similarities with the C-t erminus of the archaebacterial ribosomal A proteins. To our knowledge, this E. raikovi protein represents the first demonstration of a ribosome-associ ated protein of the PT! family in a ciliate protozoan.