The acidic ribosomal P proteins are constituents of the lateral protuberance called “stalk” of the large 60S ribosomal subunit (1). In eukaryotes this structure is composed of three types of P proteins that form the pentameric complex P0-(P1-P2)2 (2). The P0 protein, being the “stalk” base, constitutes the binding site for two protein dimers (P1-P2)2 and anchors whole pentamer to the conserved region of the 28S rRNA (3). This protein complex is a part of the GTPase-associated-center which plays main role in the ribosome-mediated stimulation of translation-factor-dependent GTP hydrolysis (4).
During biogenesis of ribosomal particles, majority of ribosomal proteins studied so far are actively transported to the nucleus/nucleolus (5), however, it seems that some proteins do not obey this rule. It looks like that the P proteins belongs to the ribosomal constituents, which do not follow the common pattern for the rest of ribosomal proteins. According to preliminary studies, the P1 and P2 proteins were mainly localized in the cytoplasmic compartment, but P0 was found in cytoplasm as well as in the nucleus (6). Additionally, nuclear localization of P0 protein was reported in complex with LCMV Z arenavirus protein, and its presence in the nucleus was not associated with the biogenesis of ribosomes (7). Therefore, we have decided to undertake analysis of the cellular distribution of the P proteins, using highly specific antibodies directed toward P0 and P1/P2 proteins. Using in situ immunodetection, we have found that P1 and P2 proteins are located in the cytoplasmic fraction. Surprisingly, the P0 protein was also localized in the cytoplasm. Other cellular compartments were excluded, what was confirmed by cell fractionation and western blotting. These findings are in disagreement with the results showing nuclear localization of P0. Therefore, in contrast to majority of ribosomal proteins, the group of P proteins behaves in different manner in the cell and they are not actively transported into the nucleus. The distribution pattern of the ribosomal stalk proteins suggests that they are assembled onto the ribosomal macromolecule in the cytoplasm compartment at a very last step of the ribosomal maturation.
1. Gonzalo, P., and Reboud, J. P. (2003) Biol Cell 95(3-4), 179-193
2. Tchorzewski, M. (2002) Int J Biochem Cell Biol 34(8), 911-915
3. Krokowski, D., Boguszewska, A., Abramczyk, D., Liljas, A., Tchorzewski, M., and Grankowski, N. (2006) Mol Microbiol 60(2), 386-400
4. Rodnina, M. V., and Wintermeyer, W. (2001) Annu Rev Biochem 70, 415-435
5. Dez, C., and Tollervey, D. (2004) Curr Opin Microbiol 7(6), 631-637
6. Tchorzewski, M., Krokowski, D., Rzeski, W., Issinger, O. G., and Grankowski, N. (2003) Int J Biochem Cell Biol 35(2), 203-211
7. Borden, K. L., Campbelldwyer, E. J., Carlile, G. W., Djavani, M., and Salvato, M. S. (1998) J Virol 72(5), 3819-3826
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