Phosphorylation of the yeast ribosomal stalk. Functional effects and enzymes involved in the process

Abstract

The ribosomal stalk is directly involved in the interaction of the elongation factors with the ribosome during protein synthesis. The stalk is formed by a complex of five proteins, four small acidic polypeptides and a larger protein which directly interacts with the rRNA at the GTPase center. In eukaryotes the acidic components correspond to the 12-kDa P1 and P2 proteins, and the RNA binding component is the P0 protein. All these proteins are found phosphorylated in eukaryotic organisms, and previous in vitro data suggested this modification was involved in the activity of this structure. Results from mutational studies have shown that phosphorylation takes place at a serine residue close to the carboxy end of the P proteins. Modification of this serine residue does not affect the formation of the stalk and the activity of the ribosome in standard conditions but induces an osmoregulation-related phenotype at 37 degrees C. The phosphorylatable serine is part of a consensus casein kinase II phosphorylation site. However, although CKII seems to be responsible for part of the stalk phosphorylation in vivo, it is probably not the only enzyme in the cell able to perform this modification. Five protein kinases, RAPI, RAPII and RAPIII, in addition to the previously reported CKII and PK60 kinases, are able to phosphorylate the stalk proteins. A comparison of the five enzymes shows differences among them that suggest some specificity regarding the phosphorylation of the four yeast acidic proteins. It has been found that some typical effectors of the PKC kinase stimulate the in vitro phosphorylation of the stalk proteins. All the data suggest that although phosphorylation is not involved in the interaction of the acidic P proteins with the ribosome, it can affect the ribosome activity and might participate in a possible ribosome regulatory mechanism.

Enrichment techniques employed in phosphoproteomics

“…Phosphorylation plays a key role in many cellular processes, including cell cycle regulation, signal transduction, cytoskeletal dynamics regulation, protein targeting, metabolism, transcription and translation regulation (Augustine et al 2008; Ballesta et al 1999; Baskaran et al 1997; Dephoure et al 2008; Fletterick and Sprang 1982; Garnak and Reeves 1979; Mishra et al 2006; Moll et al 1991; Rihs et al 1991). The most abundant amino acids that are phosphorylated are serine (pS), threonine (pT) and tyrosine (pY).…”

Ribosomal cold-adaptation: Characterization of the genes encoding the acidic ribosomal P0 and P2 proteins from the Antarctic ciliate Euplotes focardii

“…P1 and P2 share a conserved C-terminal domain and they preferentially form a (P1/P2) 2 hetero-complex recognizable as a lateral protuberance on the 60S ribosomal subunit (the so-called ribosomal stalk), with P1 as an anchor to P0. The ribosomal stalk is involved in protein synthesis regulation through interaction with soluble translation factors (Ballesta et al, 1999) and in GTP hydrolysis control during elongation steps (Liljas, 1991). P0 plays an essential role by docking the ribosomal stalk to the 26/28S rRNA (Rodriguez-Gabriel et al, 2000).…”

Phosphoproteomic identification and phylogenetic analysis of ribosomal P-proteins in Populus dormant terminal buds

“…In some eukaryotes, phosphorylation of several P-protein members occurs at the C-terminal serine (Ser) residues (Tchórzewski 2002). The conserved phosphorylation sites have been identified in humans (Molina et al 2007), rats (Moser and White 2006), and yeasts (Ballesta et al 1999). However, detailed analyses in plants have been restricted to the herbaceous species of Arabidopsis (Lin et al 1999;Carroll et al 2008;van Bentem et al 2008) and maize (Hasler et al 1991;Bailey-Serres et al 1997;Aguilar et al 1998;Szick et al 1998;Lu et al 2008).…”