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

The ribosomal protein P0A is required for embryo development in rice

BACKGROUND

The P-stalk is a conserved and vital structural element of ribosome. The eukaryotic P-stalk exists as a P0-(P1-P2)2 pentameric complex, in which P0 function as a base structure for incorporating the stalk onto 60S pre-ribosome. Prior studies have suggested that P0 genes are indispensable for survival in yeast and animals. However, the functions of P0 genes in plants remain elusive.

RESULTS

In the present study, we show that rice has three P0 genes predicted to encode highly conserved proteins OsP0A, OsP0B and OsP0C. All of these P0 proteins were localized both in cytoplasm and nucleus, and all interacted with OsP1. Intriguingly, the transcripts of OsP0A presented more than 90% of the total P0 transcripts. Moreover, knockout of OsP0A led to embryo lethality, while single or double knockout of OsP0B and OsP0C did not show any visible defects in rice. The genomic DNA of OsP0A could well complement the lethal phenotypes of osp0a mutant. Finally, sequence and syntenic analyses revealed that OsP0C evolved from OsP0A, and that duplication of genomic fragment harboring OsP0C further gave birth to OsP0B, and both of these duplication events might happen prior to the differentiation of indica and japonica subspecies in rice ancestor.

CONCLUSION

These data suggested that OsP0A functions as the predominant P0 gene, playing an essential role in embryo development in rice. Our findings highlighted the importance of P0 genes in plant development.

Functional and Mass Spectrometric Evaluation of an Anti-Tick Antigen Based on the P0 Peptide Conjugated to Bm86 Protein

A synthetic 20 amino acid peptide of the ribosomal protein P0 from ticks, when conjugated to keyhole limpet hemocyanin from Megathura crenulata and used as an immunogen against Rhipicephalus microplus and Rhipicephalus sanguineus s.l. species, has shown efficacies of around 90%. There is also experimental evidence of a high efficacy of this conjugate against Amblyomma mixtum and Ixodes ricinus species, which suggest that this antigen could be a good broad-spectrum anti-tick vaccine candidate. In this study, the P0 peptide (pP0) was chemically conjugated to Bm86 as a carrier protein. SDS-PAGE analysis of this conjugate demonstrated that it is highly heterogeneous in size, carrying from 1 to 18 molecules of pP0 per molecule of Bm86. Forty-nine out of the 54 lysine residues and the N-terminal end of Bm86 were found partially linked to pP0 by using LC-MS/MS analysis and the combination of four different softwares. Several post-translational modifications of Bm86 protein were also identified by mass spectrometry. High immunogenicity and efficacy were achieved when dogs and cattle were vaccinated with the pP0-Bm86 conjugate and challenged with R. sanguineus s.l. and R. microplus, respectively. These results encourage the development of this antigen with promising possibilities as an anti-tick vaccine.

CYTED Network to develop an immunogen compatible with integrated management strategies for tick control in cattle

INCOGARR is a thematic network recently approved to be financially supported by the Ibero-American Program of Science and Technology for Development (CYTED). The objectives of this Network are the design and evaluation of an efficient and feasible anti-tick vaccine candidate from the technical and economical points of view and also sharing experiences in the immunological control of ticks as part of an Integrated Control Program. The Network consists of seven laboratories and one company from six countries. The first meeting of the Network took place with the representation of each laboratory involved. In the meeting, general and specific objectives and activities of the Network were discussed and it was a very nice example of international collaboration to address an unsolved worldwide topic on tick control in which laboratories with different competencies and expertise join their efforts in a common goal.

Leishmania braziliensis SCD6 and RBP42 proteins, two factors with RNA binding capacity

BACKGROUND

The study of RNA binding proteins (RBPs) is of great relevance for understanding processes like post-transcriptional control of gene expression. The post-transcriptional mechanisms are particularly important in Leishmania parasites and related trypanosomatids since transcriptional regulation is almost absent in them. Thus, RBPs should be essential during the development of these parasites and for survival strategies against the adverse conditions that they face during their life-cycle. This work was aimed to do a structural and biochemical characterization of two Leishmania braziliensis proteins, which were previously found in pull-down assays using an HSP70 RNA as bait. At that time, these proteins were annotated as hypothetical proteins (LbrM.25.2210 and LbrM.30.3080) in the GeneDB database.

RESULTS

Structural analysis indicated that these two proteins belong to evolutionarily conserved families; thus, they have been renamed accordingly as LbSCD6 (LbrM.25.2210) and LbRBP42 (LbrM.30.3080). We have demonstrated experimentally that these proteins are RBPs, in agreement with their structural features. Both proteins were able to bind to the complete 3' UTR-II region of HSP70-type II mRNA, and to an A + U rich element (ARE) present in that UTR. Cellular localization assays suggested that both proteins are mainly distributed in the cytoplasm of promastigotes growing at 26 °C, but they accumulate in foci around the nucleus when the parasites are under heat-shock conditions. Also, our study showed that steady-state levels of LbSCD6 and LbRBP42 transcripts decreased significantly during incubation of L. braziliensis promastigotes at heat-shock temperatures. However, in these conditions, the cellular content of both proteins remained unaltered.

CONCLUSIONS

Our data suggest that LbSCD6 and LbRBP42, as occurs for their orthologues in other organisms, are involved in mRNA regulation, and probably they have a relevant role facing the stress conditions that L. braziliensis encounters during insect-to-mammalian transmission.

The RNA-binding protein Gemin5 binds directly to the ribosome and regulates global translation

RNA-binding proteins (RBPs) play crucial roles in all organisms. The protein Gemin5 harbors two functional domains. The N-terminal domain binds to snRNAs targeting them for snRNPs assembly, while the C-terminal domain binds to IRES elements through a non-canonical RNA-binding site. Here we report a comprehensive view of the Gemin5 interactome; most partners copurified with the N-terminal domain via RNA bridges. Notably, Gemin5 sediments with the subcellular ribosome fraction, and His-Gemin5 binds to ribosome particles via its N-terminal domain. The interaction with the ribosome was lost in F381A and Y474A Gemin5 mutants, but not in W14A and Y15A. Moreover, the ribosomal proteins L3 and L4 bind directly with Gemin5, and conversely, Gemin5 mutants impairing the binding to the ribosome are defective in the interaction with L3 and L4. The overall polysome profile was affected by Gemin5 depletion or overexpression, concomitant to an increase or a decrease, respectively, of global protein synthesis. Gemin5, and G5-Nter as well, were detected on the polysome fractions. These results reveal the ribosome-binding capacity of the N-ter moiety, enabling Gemin5 to control global protein synthesis. Our study uncovers a crosstalk between this protein and the ribosome, and provides support for the view that Gemin5 may control translation elongation.

High efficacy of a 20 amino acid peptide of the acidic ribosomal protein P0 against the cattle tick, Rhipicephalus microplus

Current strategies to control cattle ticks use integrated control programs (ICP) that include vaccination. Reduction in the use of chemicals and in the cost of tick control, the delay or elimination of acaricide resistance and the decreasing of environmental pollution are the advantages of using these programs. This integrated program is potentially applicable to all genotypes of chemical resistant ticks. However, the problem here is to improve the efficacy of anti-tick vaccines. The P0 protein is a structural component of the ribosome of all organisms. We have identified an immunogenic region of ribosomal protein P0 from Rhipicephalus spp. ticks that is not very conserved compared to the orthologous protein in their hosts. A synthetic 20 amino acid peptide from this sequence was effective as a vaccine against Rhipicephalus sanguineus infestations in an immunization and challenge experiment using rabbits. In this paper, the same peptide used as vaccine against the cattle tick Rhipicephalus Boophilus microplus shows a significant diminution in the number of engorged females recovered, in the weight of females and the weight of egg masses. The number of eggs hatched was also significantly reduced for the vaccinated group, with an overall effectivity for the antigen pP0 of 96%. These results, together with the conserved sequence of the P0 peptide among ticks, suggest that this antigen could be a good broad spectrum vaccine candidate. It would be expected to be active against many species of ticks and thus has promise in an ICP for effective control of ticks and thereby to improve the efficiency and productivity of the livestock industry.

Carboxy terminal modifications of the P0 protein reveal alternative mechanisms of nuclear ribosomal stalk assembly

The P0 scaffold protein of the ribosomal stalk is mainly incorporated into pre-ribosomes in the cytoplasm where it replaces the assembly factor Mrt4. In analyzing the role of the P0 carboxyl terminal domain (CTD) during ribosomal stalk assembly, we found that its complete removal yields a protein that is functionally similar to Mrt4, whereas a chimeric Mrt4 containing the P0 CTD behaves more like P0. Deleting the P0 binding sites for the P1 and P2 proteins provoked the nuclear accumulation of P0ΔAB induced by either leptomycin B-mediated blockage of nuclear export or Mrt4 deletion. This effect was reversed by removing P1/P2 from the cell, whereas nuclear accumulation was restored on reintroduction of these proteins. Together, these results indicate that the CTD determines the function of the P0 in stalk assembly. Moreover, they indicate that in cells lacking Mrt4, P0 and its stalk base partner, the L12 protein, bind to pre-ribosomes in the nucleus, a complex that is then exported to the cytoplasm by a mechanism assisted by the interaction with P1/P2 proteins. Furthermore, in wild-type cells, the presence of nuclear pre-ribosome complexes containing P0 but not L12 is compatible with the existence of an alternative stalk assembly process.

Ribosomal protein P0 promotes Potato virus A infection and functions in viral translation together with VPg and eIF(iso)4E

We report here that the acidic ribosomal protein P0 is a component of the membrane-associated Potato virus A (PVA) ribonucleoprotein complex. As a constituent of the ribosomal stalk, P0 functions in translation. Although the ribosomal stalk proteins P0, P1, P2, and P3 are all important for PVA infection, P0 appears to have a distinct role from those of the other stalk proteins in infection. Our results indicate that P0 also regulates viral RNA functions as an extraribosomal protein. We reported previously that PVA RNA can be targeted by VPg to a specific gene expression pathway that protects the viral RNA from degradation and facilitates its translation. Here, we show that P0 is essential for this activity of VPg, similar to eIF4E/eIF(iso)4E. We also demonstrate that VPg, P0, and eIF(iso)4E synergistically enhance viral translation. Interestingly, the positive effects of VPg and P0 on viral translation were negatively correlated with the cell-to-cell spread of infection, suggesting that these processes may compete for viral RNA.

P1 and P2 protein heterodimer binding to the P0 protein of Saccharomyces cerevisiae is relatively non-specific and a source of ribosomal heterogeneity

The ribosomal stalk is formed by four acidic phosphoproteins in Saccharomyces cerevisiae, P1α, P1β, P2α and P2β, which form two heterodimers, P1α/P2β and P1β/P2α, that preferentially bind to sites A and B of the P0 protein, respectively. Using mutant strains carrying only one of the four possible P1/P2 combinations, we found a specific phenotype associated to each P1/P2 pair, indicating that not all acidic P proteins play the same role. The absence of one P1/P2 heterodimer reduced the rate of cell growth by varying degrees, depending on the proteins missing. Synthesis of the 60S ribosomal subunit also decreased, particularly in strains carrying the unusual P1α-P2α or P1β-P2β heterodimers, although the distinct P1/P2 dimers are bound with similar affinity to the mutant ribosome. While in wild-type strains the B site bound P1β/P2α in a highly specific manner and the A site bound the four P proteins similarly, both the A and B binding sites efficiently bound practically any P1/P2 pair in mutant strains expressing truncated P0 proteins. The reported results support that while most ribosomes contain a P1α/P2β-P0-P1β/P2α structure in normal conditions, the stalk assembly mechanism can generate alternative compositions, which have been previously detected in the cell.

A novel tick antigen shows high vaccine efficacy against the dog tick, Rhipicephalus sanguineus

Ticks are acaridae ectoparasites that, while taking a blood meal, can transmit viruses, bacteria, protozoa and filarial nematodes, which cause a variety of human and animal illnesses. The use of chemical pesticides constitutes the primary measure for control of these ectoparasites. However, the intensive use of these chemicals has drawbacks such as the contamination of food, environmental pollution and development of resistance by ectoparasites. Vaccination is considered a promising alternative for controlling infestations by ectoparasites. Although emerging tick proteins have been identified recently, and have been proposed as potential targets for generating protective molecules, only a limited number of them have been evaluated in vaccine trials. More than 80 proteins are found in eukaryotic ribosomes. The protein P0 is essential for the assembly of the 60S ribosomal subunit. We have identified an immunogenic region of the ribosomal protein P0 from Rhipicephalus sp. ticks that is not very conserved compared to host P0. The efficacy of a 20 amino acid synthetic peptide from this sequence was assayed as a vaccine antigen against Rhipicephalus sanguineus infestations in an immunization and challenge experiment on rabbits. A remarkable diminution in the viability of newly molted nymphs from larvae fed on vaccinated rabbits was observed. The number of adults and the number of eggs hatching were significantly reduced, with an overall efficacy of 90%. Our results demonstrated that immunization with an immunogenic peptide of tick protein P0 greatly reduced survival of ticks, suggesting that it has promise as an effective tick control agent.

Characterization of proteome alterations in Phanerochaete chrysosporium in response to lead exposure

BACKGROUND

Total soluble proteome alterations of white rot fungus Phanerochaete chrysosporium in response to different doses (25, 50 and 100 μM) of Pb (II) were characterized by 2DE in combination with MALDI-TOF-MS.

RESULTS

Dose-dependent molecular response to Pb (II) involved a total of 14 up-regulated and 21 down-regulated proteins. The induction of an isoform of glyceraldehyde 3-phosphate dehydrogenase, alcohol dehydrogenase class V, mRNA splicing factor, ATP-dependent RNA helicase, thioredoxin reductase and actin required a Pb (II) dose of at least 50 μM. Analysis of the proteome dynamics of mid-exponential phase cells of P. chrysosporium subjected to 50 μM lead at exposure time intervals of 1, 2, 4 and 8 h, identified a total of 23 proteins in increased and 67 proteins in decreased amount. Overall, the newly induced/strongly up-regulated proteins involved in (i) amelioration of lipid peroxidation products, (ii) defense against oxidative damage and redox metabolism, (iii) transcription, recombination and DNA repair (iv) a yet unknown function represented by a putative protein.

CONCLUSION

The present study implicated the particular role of the elements of DNA repair, post-tanscriptional regulation and heterotrimeric G protein signaling in response to Pb (II) stress as shown for the first time for a basidiomycete.

Interaction map of the Trypanosoma cruzi ribosomal P protein complex (stalk) and the elongation factor 2

The large subunit of the eukaryotic ribosome possesses a long and protruding stalk formed by the ribosomal P proteins. This structure is involved in the translation step of protein synthesis through interaction with the elongation factor 2 (EF-2). The Trypanosoma cruzi stalk complex is composed of four proteins of about 11 kDa, TcP1α, TcP1β, TcP2α, TcP2β and a fifth TcP0 of about 34 kDa. In a previous work, a yeast two-hybrid (Y2H) protein-protein interaction map of T. cruzi ribosomal P proteins was generated. In order to gain new insight into the assembly of the stalk, a complete interaction map was generated by surface plasmon resonance (SPR) and the kinetics of each interaction was calculated. All previously detected interactions were confirmed and new interacting pairs were found, such as TcP1β-TcP2α and TcP1β-TcP2β. Moreover P2 but not P1 proteins were able to homo-oligomerize. In addition, the region comprising amino acids 210-270 on TcP0 was identified as the region interacting with P1/P2 proteins, using Y2H and SPR. The interaction domains on TcP2β were also mapped by SPR identifying two distinct regions. The assembly order of the pentameric complex was assessed by SPR showing the existence of a hierarchy in the association of the different P proteins forming the stalk. Finally, the TcEF-2 gene was identified, cloned, expressed and refolded. Using SPR analysis we showed that TcEF-2 bound with similar affinity to the four P1/P2 ribosomal P proteins of T. cruzi but with reduced affinity to TcP0.

The amino terminal domain from Mrt4 protein can functionally replace the RNA binding domain of the ribosomal P0 protein

In Saccharomyces cerevisiae, the Mrt4 protein is a component of the ribosome assembly machinery that shares notable sequence homology to the P0 ribosomal stalk protein. Here, we show that these proteins can not bind simultaneously to ribosomes and moreover, a chimera containing the first 137 amino acids of Mrt4 and the last 190 amino acids from P0 can partially complement the absence of the ribosomal protein in a conditional P0 null mutant. This chimera is associated with ribosomes isolated from this strain when grown under restrictive conditions, although its binding is weaker than that of P0. These ribosomes contain less P1 and P2 proteins, the other ribosomal stalk components. Similarly, the interaction of the L12 protein, a stalk base component, is affected by the presence of the chimera. These results indicate that Mrt4 and P0 bind to the same site in the 25S rRNA. Indeed, molecular dynamics simulations using modelled Mrt4 and P0 complexes provide further evidence that both proteins bind similarly to rRNA, although their interaction with L12 displays notable differences. Together, these data support the participation of the Mrt4 protein in the assembly of the P0 protein into the ribosome and probably, that also of the L12 protein.

KIF4 mediates anterograde translocation and positioning of ribosomal constituents to axons

In this study, we have used a combination of biochemical and molecular biology techniques to demonstrate that the C-terminal tail domain of KIF4 directly interacts with P0, a major protein component of ribosomes. Besides, in dorsal root ganglion neurons, KIF4 and P0, as well as other ribosomal constituents, colocalize in clusters distributed along axons and neuritic tips. RNA interference suppression of KIF4 or expression of KIF4 variants lacking the tail domain or mutations of the ATP-binding site result in accumulation of P0 and other ribosomal proteins at the cell body and in their disappearance from axons. Our results also show one additional function for KIF4 involving an Ezrin-Radixin-Moesin-like domain in the second coiled-coiled region of KIF4. Expression of a KIF4 mutant lacking this domain abolishes the clustering of ribosomal constituents and prevents the anterograde translocation of the cell adhesion molecule L1. Taken together, the present results suggest that by binding to P0 through its tail domain and by using its motor activity, KIF4 is involved in the anterograde trafficking of ribosomal constituents to axons and that by means of its Ezrin-Radixin-Moesin-like domain interacts and transports L1.

The RACK1 signal anchor protein from Trypanosoma brucei associates with eukaryotic elongation factor 1A: a role for translational control in cytokinesis

RACK1 is a WD-repeat protein that forms signal complexes at appropriate locations in the cell. RACK1 homologues are core components of ribosomes from yeast, plants and mammals. In contrast, a cryo-EM analysis of trypanosome ribosomes failed to detect RACK1, thus eliminating an important translational regulatory mechanism. Here we report that TbRACK1 from Trypanosoma brucei associates with eukaryotic translation elongation factor-1a (eEF1A) as determined by tandem MS of TAP-TbRACK1 affinity eluates, co-sedimentation in a sucrose gradient, and co-precipitation assays. Consistent with these observations, sucrose gradient purified 80S monosomes and translating polysomes each contained TbRACK1. When RNAi was used to deplete cells of TbRACK1, a shift in the polysome profile was observed, while the phosphorylation of a ribosomal protein increased. Under these conditions, cell growth became hypersensitive to the translational inhibitor anisomycin. The kinetoplasts and nuclei were misaligned in the postmitotic cells, resulting in partial cleavage furrow ingression during cytokinesis. Overall, these findings identify eEF1A as a novel TbRACK1 binding partner and establish TbRACK1 as a component of the trypanosome translational apparatus. The synergy between anisomycin and TbRACK1 RNAi suggests that continued translation is required for complete ingression of the cleavage furrow.

cDNA cloning and overexpression of acidic ribosomal phosphoprotein P1 gene (RPLP1) from the giant panda

RPLP1 is one of acidic ribosomal phosphoproteins encoded by RPLP1 gene, which plays an important role in the elongation step of protein synthesis. The cDNA of RPLP1 was cloned successfully for the first time from the Giant Panda (Ailuropoda melanoleuca) using RT-PCR technology, which was also sequenced, analyzed preliminarily and expressed in E.coli. The cDNA fragment cloned is 449bp in size, containing an open reading frame of 344bp encoding 114 amino acids. Alignment analysis indicated that the nucleotide sequence and the deduced amino acid sequence are highly conserved to other five species studied, including Homo sapiens, Mus musculus, Rattus norvegicus, Bos Taurus and Sus scrofa. The homologies for nucleotide sequences of Giant Panda PPLP1 to that of these species are 92.4%, 89.8%, 89.0%, 91.3% and 87.5%, while the homologies for amino acid sequences are 96.5%, 94.7%, 95.6%, 96.5% and 88.6%. Topology prediction showed there are three Casein kinase II phosphorylation sites and two N-myristoylation sites in the RPLP1 protein of the Giant Panda (Ailuropoda melanoleuca). The RPLP1 gene was overexpressed in E. coli and the result indicated that RPLP1 fusion with the N-terminally His-tagged form gave rise to the accumulation of an expected 18kDa polypeptide, which was in accordance with the predicted protein and could also be used to purify the protein and study its function.

In vivo analysis of the acidic ribosomal proteins BmP1 and BmP2 of the silkworm Bombyx mori in the yeast Saccharomyces cerevisiae

In the silkworm Bombyx mori the ribosomal stalk P-protein family consists of two low MW acidic proteins, BmP1 and BmP2, and of one higher MW protein, BmP0, as shown by electrophoretical and immunoblotting western blot analysis of purified ribosomes. Treatment of ribosomes with alkaline phosphatase followed by electrofocusing shifted the isoelectric points to higher pH, implying phosphorylation of the proteins. The cDNAs encoding BmP1 and BmP2 proteins were constructed and expressed in the Saccharomyces cerevisiae mutant strains defective in either the endogenous P1 or P2 proteins. The recombinant silkworm proteins could complement the absence of the homologous yeast proteins and were incorporated to the ribosomes of the transformed strains, helping the binding of the remaining endogenous acidic proteins, present in the cytoplasm in different extent. Thus, BmP1 was able to replace YP1alpha, preferentially binding YP2beta to the ribosome, while BmP2 replaced both yeast P2 proteins and induced the binding of both YP1alpha and YP1beta.

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

Molecular adaptation at low temperature requires specificities represented mainly by modifications in the gene sequence and consequently in the protein primary structure. To characterize the molecular mechanisms responsible for ribosome cold-adaptation, we compared the ribosomal P0 and P2 genes from the Antarctic ciliate Euplotes focardii with homologous genes from mesophilic organisms, including the ciliates Tetrahymena thermophila and non cold-adapted Euplotes species. This analysis revealed the presence of non synonymous mutations unique to E. focardii. In the P0 protein the mutations produced amino acid substitutions that increased the molecular flexibility that may facilitate a conformational adjustment associated with the interaction with the GTPase center of the large subunit rRNA, and increased the hydrophobicity of the region involved in the interaction with P1/P2 heterodimer, probably to keep associated the ribosomal stalk in the cold. In the P2 protein the mutations produced amino acid substitutions that increased the N-terminus flexibility, which may facilitate interactions with P1 protein in the formation of the heterodimer, and reduced the mobility of the C-terminus, to stabilize the stalk during ribosomal activity. Finally, P proteins appeared to be valid markers for investigating the phylogenetic origin of early eukaryotes.

Characterization of the 26S rRNA-binding domain in Saccharomyces cerevisiae ribosomal stalk phosphoprotein P0

The stalk is a universal structure of the large ribosomal subunit involved in the function of translation factors. The bacterial stalk is highly stable but its stability is notably reduced in eukaryotes, favouring a translation regulatory activity of this ribosomal domain, which has not been reported in prokaryotes. The RNA-binding protein P0 plays a key role in determining the eukaryotic stalk activities, and characterization of the P0/RNA interaction is essential to understand the evolutionary process. Using a series of Saccharomyces cerevisiae-truncated proteins, a direct involvement of two N-terminal regions, I3-M58 and K81-V121, in the interaction of P0 with the ribosome has been shown. Two other conserved regions, R122-T149 and G162-T182, affect P0 interaction with other stalk components and the sensitivity to sordarin anti-fungals but are not essential for RNA binding. Moreover, P0 and a P0 fragment comprising only the first 121 amino acids show a similar in vitro affinity for the highly conserved 26S rRNA binding site. A protein chimera containing the first 165 amino acids of L10, the P0 bacterial counterpart, is able to complement the absence of P0 and also shows the same P0 RNA binding characteristics. Altogether, the results indicate that the affinity of the stalk RNA-binding protein for its substrate has been highly conserved, and changes in the stability of the interaction of P0 with the ribosome, which are essential for the new eukaryotic functions, result from the evolution of the overall stalk structure.

Functional complementation of yeast ribosomal P0 protein with Plasmodium falciparum P0

A complex of three phosphoproteins (P0, P1 and P2) constitutes the stalk region at the GTPase center of the eukaryotic large ribosomal subunit, amongst which the protein P0 plays the most crucial role. Earlier studies have shown the functional complementation of the conditional P0-null mutant of Saccharomyces cerevisiae (W303dGP0) with orthologous P0 genes from fungal and mammalian organisms, but not the protozoan parasite Leishmania infantum. In this paper we show that the PfP0 gene from the protozoan malaria parasite Plasmodium falciparum can functionally complement the conditional P0-null W303dGP0 mutant of S. cerevisiae. Unlike the above orthologous genes, PfP0 gene could also rescue the D67dGP0 strain, which in addition to being a conditional null for ScP0 gene, is a null-mutant for both ScP1alpha and beta genes. However, under stress conditions such as high temperature, salt and osmolarity, PfP0 gene could not rescue D67dGP0 strain. Ribosomes purified from W303dGP0 carrying PfP0 gene did not contain ScP1 protein, indicating a lack of binding of ScP1 to PfP0 protein. Yeast 2-hybrid analysis further confirmed the lack of binding of ScP1 to PfP0 protein. The polymerizing activities of ribosomes with ScP0 or PfP0 protein, in the absence of ScP1 protein, were found to be about 40-45% that of ribosomes with all the yeast P-proteins. In its sensitivity to the inhibitor sordarin, PfP0 was similar to the P0 protein from the fungus Aspergillus fumigatus. These results indicate a closer functional relationship of P. falciparum P0 gene to fungal P0 genes.

Expression and significance of tumor-related genes in HCC

AIM: To investigate the expression and clinical significance of DEK, cyclin D1, insulin-like growth factor II (IGF-II), glypican 3 (GPC3), ribosomal phosphoprotein 0 (rpP0) mRNA in hepatocellular carcinoma (HCC) and its paraneoplastic tissues.

METHODS: The expression of mRNAs of DEK, cyclin D1, IGF-II, GPC3 and rpP0 mRNA was detected in HCC and its paraneoplastic tissues by multiplex RT-PCR.

RESULTS: By the simplex RT-PCR, the overexpression of mRNAs of DEK, cyclin D1, IGF-II, GPC3, rpP0 mRNA in HCC and its paraneoplastic tissues was 78.1%, 87.5%, 87.5%, 75.0%, 81.3% and 15.6%, 40.6%, 37.5%, 21.9%, 31.3% respectively (P < 0.05). By the multiplex RT-PCR, at least one of the mRNAs was detected in all HCC samples and in 75.0% of paraneoplastic samples (P > 0.05). However, all these five mRNAs were found in 68.8% of HCC samples, but only in 9.4% of paraneoplastic tissues (P < 0.05). The positive expression of mRNAs of DEK, cyclin D1, IGF-II, GPC3, rpP0 in well- and poorly-differentiated HCC was 89.0%, 66.7%, 66.7%, 66.7%, 77.8% and 73.9%, 95.7%, 95.7%, 95.7%, 82.6%, respectively (P > 0.05). The expression of these genes in HCCs with α-feto protein (AFP) negative and positive was 90.0%, 80.0%, 90.0%, 90.0%, 90.0% and 72.7%, 86.3%, 77.3%, 90.9%, 68.2% respectively (P > 0.05).

CONCLUSION: The expression of DEK, cyclin D1, IGF-II, GPC3, rpP0 mRNA in HCC is much higher in HCC than in its paraneoplastic tissues. Multiplex RT-PCR assay is an effective, sensitive, accurate, and cost-effective diagnostic method of HCC.

Mass Spectrometry of Ribosomes from Saccharomyces cerevisiae

The acidic ribosomal P proteins form a distinct protuberance on the 60 S subunit of eukaryotic ribosomes. In yeast this structure is composed of two heterodimers (P1alpha-P2beta and P1beta-P2alpha) attached to the ribosome via P0. Although for prokaryotic ribosomes the isolation of a pentameric stalk complex comprising the analogous proteins is well established, its observation has not been reported for eukaryotic ribosomes. We used mass spectrometry to examine the composition of the stalk proteins on ribosomes from Saccharomyces cerevisiae. The resulting mass spectra reveal a noncovalent complex of mass 77,291 +/- 7 Da assigned to the pentameric stalk. Tandem mass spectrometry confirms this assignment and is consistent with the location of the P2 proteins on the periphery of the stalk complex, shielding the P1 proteins, which in turn interact with P0. No other oligomers are observed, confirming the specificity of the pentameric complex. At lower m/z values the spectra are dominated by individual proteins, largely from the stalk complex, giving rise to many overlapping peaks. To define the composition of the stalk proteins in detail we compared spectra of ribosomes from strains in which genes encoding either or both of the interacting stalk proteins P1alpha or P2beta are deleted. This enables us to define novel post-translational modifications at very low levels, including a population of P2alpha molecules with both phosphorylation and trimethylation. The deletion mutants also reveal interactions within the heterodimers, specifically that the absence of P1alpha or P2beta destabilizes binding of the partner protein on the ribosome. This implies that assembly of the stalk complex is not governed solely by interactions with P0 but is a cooperative process involving binding to partner proteins for additional stability on the ribosome.

Ribosomal P0 protein domain involved in selectivity of antifungal sordarin derivatives

The ribosomal stalk protein P0 is involved in the susceptibility to the antifungal sordarin derivatives, as reported for a number of Saccharomyces cerevisiae resistant mutants. Mammals and some lower eukaryotes are naturally resistant to these compounds. It is shown here that expression in S. cerevisiae of the ribosomal protein P0 from Homo sapiens and from other sordarin-resistant organisms results in a decrease in the sensitivity of the cells to an agent of this class. To further characterize the P0 region responsible for inducing sordarin resistance, a series of protein chimeras containing complementary regions of the human and yeast P0 proteins were constructed and expressed in yeast. The chimeras complement the absence of the native yeast P0 except in chimeras containing the human P0 carboxyl-terminal domain. Resistance to sordarins was found to be associated with the presence of an HsP0 amino acid sequence comprising P118 to F138, which unexpectedly led to higher resistance than the presence of the complete human P0. A comparison of the corresponding region in P0 from yeast and sordarin-insensitive organisms, followed by site-directed mutagenesis, indicates that residues in positions 119, 124, and 126 have an important role in determining resistance to sordarins. Moreover, since sordarins block the eukaryotic elongation factor 2 (EF2) function, the P0 region affecting sordarin susceptibility must correspond to EF2-interacting domains of the ribosomal stalk protein, which affects the drug-binding site in the elongation factor.

Tag-mediated fractionation of yeast ribosome populations proves the monomeric organization of the eukaryotic ribosomal stalk structure

The analysis of the not well understood composition of the stalk, a key ribosomal structure, in eukaryotes having multiple 12 kDa P1/P2 acidic protein components has been approached using these proteins tagged with a histidine tail at the C-terminus. Tagged Saccharomyces cerevisiae ribosomes, which contain two P1 proteins (P1 alpha and P1 beta) and two P2 proteins (P2 alpha and P2 beta), were fractionated by affinity chromatography and their stalk composition was determined. Different yeast strains expressing one or two tagged proteins and containing either a complete or a defective stalk were used. No indication of protein dimers was found in the tested strains. The results are only compatible with a stalk structure containing a single copy of each one of the four 12 kDa proteins per ribosome. Ribosomes having an incomplete stalk are found in wild-type cells. When one of the four proteins is missing, the ribosomes do not carry the three remaining proteins simultaneously, containing only two of them distributed in pairs made of one P1 and one P2. Ribosomes can carry two, one or no acidic protein pairs. The P1 alpha/P2 beta and P1beta/P2 alpha pairs are preferentially found in the ribosome, but they are not essential either for stalk assembly or function.

Overexpression, purification and characterization of the acidic ribosomal P-proteins from Candida albicans

In all eukaryotic cells, acidic ribosomal P-proteins form a lateral protuberance on the 60S ribosomal subunit-the so-called stalk-structure that plays an important role during protein synthesis. In this work, we report for the first time a full-length cloning of four genes encoding the P-proteins from Candida albicans, their expression in Escherichia coli, purification and characterization of the recombinant proteins. Considerable amino acid sequence similarity was found between the cloned proteins and other known fungal ribosomal P-proteins. On the basis of their phylogenetic relationship and amino acid similarity to their yeast counterparts, the C. albicans P-proteins were named P1A, P1B, P2A and P2B. Using three different approaches, namely: chemical cross-linking method, gel filtration and two-hybrid system, we analyzed mutual interactions among the C. albicans P-proteins. The obtained data showed all the four P-proteins able to form homo-oligomeric complexes. However, the ones found between P1B-P2A and P1A-P2B were dominant forms among the C. albicans P-proteins. Moreover, the strength of interactions between particular proteins was different in these two complexes; the strongest interactions were observed between P1B and P2A proteins, and a significantly weaker one between P1A and P2B proteins.

Cloning and sequencing of a cDNA expressing a ribosomal P0 peptide from Culicoides nubeculosus (Diptera)

Insect bite dermal hypersensitivity (IBH) is an allergic dermatitis of horses caused by bites of Culicoides spp. and sometimes Simulium spp. The aim of the investigation presented here was to identify allergens causing IBH. A cDNA library expressing recombinant Culicoides nubeculosus proteins was screened using affinity-purified serum from an IBH-affected horse. Screening of the library resulted in identification of one immunoreactive clone. The sequence of the cDNA insert was determined and revealed a 600 bp insert with an open reading frame coding for a 78 amino acid long protein, called rCul n 1. Analysis of the deduced amino acid sequence revealed an identity of 67-78% to the C-terminal part of the 318 amino acid long ribosomal P0 protein from other Diptera. Furthermore, the 38 C-terminal amino acids displayed an identity of 57% with the C-terminal part of the acidic ribosomal protein P2 from Aspergillus fumigatus. The cDNA insert was subcloned and expressed as a [His]6-tagged protein in Escherichia coli and purified using Ni2(+)-chelate affinity chromatography. The 10kDa recombinant Cul n 1 protein bound the affinity-purified antibody fraction used for screening the expression library. Determination of IgE and IgG levels against rCul n 1 by ELISA in sera from 19 IBH-affected and 18 Swiss control horses and in sera from eight control horses living in Iceland showed no significant differences between the three groups of horses (median IgE levels = 60, 49 and 44 relative ELISA units, respectively). rCul n 1 did not induce sulfidoleukotriene (sLT) release from peripheral blood leukocytes of IBH-affected horses (N = 5), although sLT release was induced with the Culicoides whole body extract.

Identification of a hypothetical membrane protein interactor of ribosomal phosphoprotein P0

The ribosomal phosphoprotein P0 of the human malarial parasite Plasmodium falciparum (PfP0) has been identified as a protective surface protein. In Drosophila, P0 protein functions in the nucleus. The ribosomal function of P0 is mediated at the stalk of the large ribosomal subunit at the GTPase centre, where the elongation factor eEF2 binds. The multiple roles of the P0 protein presumably occur through interactions with other proteins. To identify such interacting protein domains, a yeast two-hybrid screen was carried out. Out of a set of sixty clones isolated, twelve clones that interacted strongly with both PfP0 and the Saccharomyces cerevisiae P0 (ScP0) protein were analysed. These belonged to three broad classes: namely (i) ribosomal proteins; (ii) proteins involved in nucleotide binding; and (iii) hypothetical integral membrane proteins. One of the strongest interactors (clone 67B) mapped to the gene YFL034W which codes for a hypothetical integral membrane protein, and is conserved amongst several eukaryotic organisms. The insert of clone 67B was expressed as a recombinant protein, and immunoprecipitaion (IP) reaction with anti-P0 antibodies pulled down this protein along with PfP0 as well as ScP0 protein. Using deletion constructions, the domain of ScP0, which interacted with clone 67B, was mapped to 60-148 amino acids. It is envisaged that the surface localization of P0 protein may be mediated through interactions with putative YFL034W-like proteins in P. falciparum.

Protein BmP0 from the silkworm Bombyx mori can be assembled and is functional in the Saccharomyces cerevisiae ribosomal stalk in the absence of the acidic P1 and P2 proteins

The DNA complementary to RNA (cDNA) of the ribosomal stalk protein BmP0 of the silkworm Bombyx mori was isolated from a cDNA library and was subsequently expressed in the conditional P0-null mutant Saccharomyces cerevisiae D67dGP0, whose ribosomes also lack the other stalk components, proteins P1/P2. The transformed strain was able to grow under restrictive conditions, indicating that in the absence of the P1/P2 proteins BmP0 can bind to the yeast ribosomes and complement the lack of the endogenous YP0 protein. In addition, the binding capacity of the B. mori ribosomal stalk components to the ribosomal particle was studied by means of high salt treatment of purified ribosomes. The BmP0 protein retained its binding to the ribosome, suggesting a stable association with the rRNA, in contrast to the acidic proteins BmP1 and BmP2, which were easily released. The results clearly indicate that, as opposed to recent in vitro results, BmP0 does not require the presence of P1/P2 proteins in order to bind to the ribosome.

Rpn6p, a proteasome subunit from Saccharomyces cerevisiae, is essential for the assembly and activity of the 26 S proteasome

We report the functional characterization of RPN6, an essential gene from Saccharomyces cerevisiae encoding the proteasomal subunit Rpn6p. For this purpose, conditional mutants that are able to grow on galactose but not on glucose were obtained. When these mutants are shifted to glucose, Rpn6p depletion induces several specific phenotypes. First, multiubiquitinated proteins accumulate, indicating a defect in proteasome-mediated proteolysis. Second, mutant yeasts are arrested as large budded cells with a single nucleus and a 2C DNA content; in addition, the spindle pole body is duplicated, indicating a general cell cycle defect related to the turnover of G(2)-cyclins after DNA synthesis. Clb2p and Pds1p, but not Sic1p, accumulate in the arrested cells. Depletion of Rpn6p affects both the structure and the peptidase activity of proteasomes in the cell. These results implicate Rpn6p function in the specific recognition of a subset of substrates and point to a role in maintaining the correct quaternary structure of the 26 S proteasome.

Characterization of interaction sites in the Saccharomyces cerevisiae ribosomal stalk components

The interactions among the yeast stalk components (P0, P1alpha, P1beta, P2alpha and P2beta) and with EF-2 have been explored using immunoprecipitation, affinity chromatography and the two-hybrid system. No stable association was detected between acidic proteins of the same type. In contrast, P1alpha and P1beta were found to interact with P2beta and P2alpha respectively. An interaction of P0 with P1 proteins, but not with P2 proteins, was also detected. This interaction is strongly increased with the P0 carboxyl end, which is able to form a pentameric complex with the four acidic proteins. The P1/P2 binding site has been located between residues 212 and 262 using different C-terminal P0 fragments. Immunoprecipitation shows the association of EF-2 with protein P0. However, the interaction is stronger with the P1/P2 proteins than with P0 in the two-hybrid assay. This interaction improves using the 100-amino-acid-long C-end of P0 and is even higher with the last 50 amino acids. The data indicate a specific association of P1alpha with P2beta and of P1beta with P2alpha rather than the dimerization of the acidic proteins found in prokaryotes. In addition, they suggest that stalk assembly begins by the interaction of the P1 proteins with P0. Moreover, as functional interactions of the complete P0 were found to increase using protein fragments, the data suggest that some active sites are exposed in the ribosome as a result of conformational changes that take place during stalk assembly and function.

Interaction among silkworm ribosomal proteins P1, P2 and P0 required for functional protein binding to the GTPase-associated domain of 28S rRNA

Acidic ribosomal phosphoproteins P0, P1 and P2 were isolated in soluble form from silkworm ribosomes and tested for their interactions with each other and with RNA fragments corresponding to the GTPase-associated domain of residues 1030-1127 (Escherichia coli numbering) in silkworm 28S rRNA in vitro. Mixing of P1 and P2 formed the P1-P2 heterodimer, as demonstrated by gel mobility shift and chemical crosslinking. This heterodimer, but neither P1 or P2 alone, tightly bound to P0 and formed a pentameric complex, presumably as P0(P1-P2)2, assumed from its molecular weight derived from sedimentation analysis. Complex formation strongly stimulated binding of P0 to the GTPase-associated RNA domain. The protein complex and eL12 (E.coli L11-type), which cross-bound to the E.coli equivalent RNA domain, were tested for their function by replacing with the E.coli counterparts L10.L7/L12 complex and L11 on the rRNA domain within the 50S subunits. Both P1 and P2, together with P0 and eL12, were required to activate ribosomes in polyphenylalanine synthesis dependent on eucaryotic elongation factors as well as eEF-2-dependent GTPase activity. The results suggest that formation of the P1-P2 heterodimer is required for subsequent formation of the P0(P1-P2)2 complex and its functional rRNA binding in silkworm ribosomes.

Role of the ribosomal stalk components in the resistance of Aspergillus fumigatus to the sordarin antifungals

Aspergillus fumigatus, an important human nosocomial pathogen, is resistant to sordarin derivatives, a new family of antifungals that inhibit protein synthesis by interaction with the EF-2-ribosomal stalk complex. To explore the role of the A. fumigatus ribosome in the resistance mechanism, the fungal stalk proteins were biochemically and genetically characterized and expressed in the sensitive Saccharomyces cerevisiae. Two acidic phosphoproteins homologous to the 12 kDa P1 and P2 proteins described in other organisms were found together with the 34 kDa P0 protein, the third stalk component. The genes encoding each fungal stalk protein were expressed in mutant S. cerevisiae strains lacking the equivalent proteins. Both AfP1 and AfP2 proteins interact with their yeast counterparts of the opposite type and bind to the ribosomal particles in the presence of either the S. cerevisiae or the A. fumigatus P0 protein. The A. fumigatus acidic phosphoproteins did not alter the yeast ribosome sordarin sensitivity. On the contrary, the presence of the fungal P0 induces in vivo and in vitro resistance to sordarin derivatives when present in the yeast ribosome. The mutations A117-->E, P122-->R and G124-->V in A. fumigatus P0 reduce the resistance capacity of the protein. An S. cerevisiae strain with the complete ribosomal stalk of A. fumigatus was obtained, which could be useful for the screening of new antifungals against this pathogenic fungus.

Asymmetric interactions between the acidic P1 and P2 proteins in the Saccharomyces cerevisiae ribosomal stalk

The Saccharomyces cerevisiae ribosomal stalk is made of five components, the 32-kDa P0 and four 12-kDa acidic proteins, P1alpha, P1beta, P2alpha, and P2beta. The P0 carboxyl-terminal domain is involved in the interaction with the acidic proteins and resembles their structure. Protein chimeras were constructed in which the last 112 amino acids of P0 were replaced by the sequence of each acidic protein, yielding four fusion proteins, P0-1alpha, P0-1beta, P0-2alpha, and P0-2beta. The chimeras were expressed in P0 conditional null mutant strains in which wild-type P0 is not present. In S. cerevisiae D4567, which is totally deprived of acidic proteins, the four fusion proteins can replace the wild-type P0 with little effect on cell growth. In other genetic backgrounds, the chimeras either reduce or increase cell growth because of their effect on the ribosomal stalk composition. An analysis of the stalk proteins showed that each P0 chimera is able to strongly interact with only one acidic protein. The following associations were found: P0-1alpha.P2beta, P0-1beta.P2alpha, P0-2alpha.P1beta, and P0-2beta.P1alpha. These results indicate that the four acidic proteins do not form dimers in the yeast ribosomal stalk but interact with each other forming two specific associations, P1alpha.P2beta and P1beta.P2alpha, which have different structural and functional roles.

Overexpression and refolding of the hydrophobic ribosomal P0 protein from Trypanosoma cruzi: a component of the P1/P2/P0 complex

The P0 protein is part of the ribosomal eukaryotic stalk, which is an elongated lateral protuberance of the large ribosomal subunit involved in the translocation step of protein synthesis. P0 is the minimal portion of the stalk that is able to support accurate protein synthesis. The P0 C-terminal peptide is highly antigenic and a major target of the antibody response in patients with systemic lupus erythematosus and patients suffering chronic heart disease produced by the Trypanosoma cruzi parasite. The T. cruzi P0 (TcP0) protein was cloned into the pRSET A vector and expressed in Escherichia coli fused to a His-tag. The identity of the protein was confirmed by immunoblotting. Due to the formation of inclusion bodies the protein was purified using the following steps: (i) differential centrifugation to separate the inclusion bodies from soluble proteins and (ii) affinity chromatography under denaturing conditions. TcP0 showed high tendency to aggregation during refolding assays. However, TcP0 could be efficiently folded in the presence of a low concentration of SDS. The folding of the protein was confirmed using urea gradient electrophoresis, limited proteolysis, circular dichroism, and tryptophan fluorescence. Native electrophoresis showed that the folded TcP0 (and not a folding intermediate) was the cause of aggregation in the absence of SDS. The protocol described here permitted us to obtain large amounts (up to 30 mg per culture liter) of pure and folded TcP0, a very hydrophobic protein with a high tendency to aggregation.

Trichosanthin interacts with acidic ribosomal proteins P0 and P1 and mitotic checkpoint protein MAD2B

Trichosanthin is a ribosome-inactivating protein with multiple pharmacological properties. By a yeast two-hybrid system, ribosomal phosphoproteins P0 and P1 and a putative mitotic checkpoint protein, MAD2B, were found to interact with an active-site mutated trichosanthin (TCS). The interactions were verified by an in vitro binding assay of recombinant wild-type TCS and target proteins. The interaction domain of P0 was mapped to amino acids 220-273, which had been previously reported to be involved in the interaction with P1 and P2 in yeast. Consistent with our previous finding that the last seven residues of TCS are not essential for an active conformation, the same deletion did not affect the interaction with P0. Our present study suggests that TCS may disrupt the binding of elongation factors to the P-complex, in addition to the well-known N-glycosidase activity for ribosome inactivation.

Oligomerization properties of the acidic ribosomal P-proteins from Saccharomyces cerevisiae: effect of P1A protein phosphorylation on the formation of the P1A-P2B hetero-complex

Acidic ribosomal P-proteins form, in all eukaryotic cells, a lateral protuberance, the so-called 'stalk', which is directly involved in translational activity of the ribosomes. In Saccharomyces cerevisiae cells, there are four distinct P-proteins: P1A, P1B, P2A and P2B. In spite of the high level of their structural homology, they are not completely equivalent and may perform different functions. As yet, the protein-protein interactions between yeast P-proteins have not been fully defined. In this paper, the interplay between yeast P-proteins has been investigated by means of a two-hybrid system, chemical cross-linking and gel filtration. The data presented herein show that all P-proteins are able to form homo-oligomeric complexes. By analyzing hetero-interactions, we were able to detect strong interactions between P1A and P2B proteins. Additionally, the pair of P1B and P2A proteins is also able to form a hetero-complex, though at a very low efficiency. All P-proteins are phosphorylated by numerous protein kinases. Using the multifunctional protein kinase CK II, we have shown that incorporation of phosphate into P1A protein can exert its effect on the hetero-oligomerization process, namely by preventing the formation of the hetero-oligomer P1A-P/P2B. These findings are the first to show differences in the oligomerization behavior of the yeast P-proteins; moreover, they emphasize a significant impact of the phosphorylation on the formations of P-protein complex.

Conformational changes induced in the Saccharomyces cerevisiae GTPase-associated rRNA by ribosomal stalk components and a translocation inhibitor

The yeast ribosomal GTPase associated center is made of parts of the 26S rRNA domains II and VI, and a number of proteins including P0, P1alpha, P1beta, P2alpha, P2beta and L12. Mapping of the rRNA neighborhood of the proteins was performed by footprinting in ribosomes from yeast strains lacking different GTPase components. The absence of protein P0 dramatically increases the sensitivity of the defective ribosome to degradation hampering the RNA footprinting. In ribosomes lacking the P1/P2 complex, protection of a number of nucleotides is detected around positions 840, 880, 1100, 1220-1280 and 1350 in domain II as well as in several positions in the domain VI alpha-sarcin region. The protection pattern resembles the one reported for the interaction of elongation factors in bacterial systems. The results exclude a direct interaction of these proteins with the rRNA and are compatible with an increase in the ribosome affinity for EF-2 in the absence of the acidic P proteins. Interestingly, a sordarin derivative inhibitor of EF-2 causes an opposite effect, increasing the reactivity in positions protected by the absence of P1/P2. Similarly, a deficiency in protein L12 exposes nucleotides G1235, G1242, A1262, A1269, A1270 and A1272 to chemical modification, thus situating the protein binding site in the most conserved part of the 26S rRNA, equivalent to the bacterial protein L11 binding site.

Phosphorylation and N-terminal region of yeast ribosomal protein P1 mediate its degradation, which is prevented by protein P2

The stalk proteins P1 and P2, which are fundamental for ribosome activity, are the only ribosomal components for which there is a cytoplasmic pool. Accumulation of these two proteins is differentially regulated in Saccharomyces cerevisiae by degradation. In the absence of P2, the amount of P1 is drastically reduced; in contrast, P2 proteins are not affected by a deficiency in P1. However, association with P2 protects P1 proteins. The half-life of P1 is a few minutes, while that of P2 is several hours. The proteasome is not involved in the degradation of P1 proteins. The different sensitivity to degradation of these two proteins is associated with two structural features: phosphorylation and N-terminus structure. A phosphorylation site at the C-terminus is required for P1 proteolysis. P2 proteins, despite being phosphorylated, are protected by their N-terminal peptide. An exchange of the first five amino acids between the two types of protein makes P1 resistant and P2 sensitive to degradation.