The acidic ribosomal proteins as regulators of the eukaryotic ribosomal activity

Sáenz-Robles, Maria Teresa; Remacha, Miguel; Vilella, Maria Dolores; Zínker, Samuel; Ballesta, Juan P. G.

doi:10.1016/0167-4781(90)90140-w

Cited by 84 publications

(92 citation statements)

References 20 publications

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“…In the fast-growing cells, there are 40% more ribosomal acid proteins than in cells from the stationary phase of growth. Polysomes are also richer in acidic proteins than monosomes [48]. If we assume that the presence of acidic proteins in the active structure of the ribosome depends on their phosphorylation state, the results in this paper are compatible because the quantity of the 60s kinase in the fast-growing yeast cells is much greater than in cells from other growth phases (Fig.…”

Section: Discussionsupporting

confidence: 77%

Specfic protein kinase from Saccharomyces cerevisiae cells phosphorylating 60S ribosomal proteins

Pilecki

Grankowski

Jacobs

et al. 1992

European Journal of Biochemistry

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A protein kinase, specific for 60s ribosomal proteins, has been isolated from Saccharomyces cerevisiae cells, purified to almost homogeneity and characterized. The isolated enzyme is not related to other known protein kinases. Enzyme purification comprised three chromatography steps ; DEAEcellulose, phosphocellulose and heparin -Sepharose. SDSjPAGE analysis of the purified enzyme, indicated a molecular mass of around 71 kDa for the stained single protein band. The specific activity of the protein kinase was directed towards the 60s ribosomal proteins L44, L44, L45 and a 38 kDa protein. All the proteins are phosphorylated only at the serine residues. None of the 40s ribosomal proteins were phosphorylated in the presence of the kinase. For that reason we have named the enzyme the 60s kinase. An analysis of the phosphopeptide maps of acidic ribosomal proteins, phosphorylated at either the 60s kinase or casein kinase 11, showed almost identical patterns. Using the immunoblotting technique, the presence of the kinase has been detected in extracts obtained from intensively growing cells. These findings suggest an important role played by the 60s kinase in the regulation of ribosomal activity during protein synthesis. 20 years ago, when Kaltschmidt and Wittmann described the gel electrophoresis procedure for the separation and identification of Escherichia coli ribosomal proteins [l], the two acidic proteins L7 and L12 (12 kDa) of the 50s subunit have become one of the most studied ribosomal proteins with respect to their three-dimensional structure and biological function.The functional and physicochemical equivalents of the procaryotic L7 and L12 are two ribosomal proteins, L44 and L45, from the eucaryotic 60s subunit (for review see [2]). Contrary to in animals, the ribosomes of Saccharomyces cerevisiae cells contain a third low-molecular-mass acidic protein. That protein, named L44', can be separated on DEAEcellulose [3] and by an electrofocusing procedure in acrylamide gel [4]. All three proteins have molecular masses of about 13 kDa, belong to 'split proteins ' [5] The phosphorylation of the crude eucaryotic ribosomes was initially reported by Kabat [lo] and by Loeb et al. [ll]. Later studies by other authors have shown that mammalian ribosomes are associated with cyclic-AMP-independent protein kinases [12-151. One of the enzymes has turned out to be a casein kinase type I1 (CKII) which phosphorylates proteins L44 and L45 [14]. For the yeast ribosomes, it has been found that the majority of phosphoproteins, y-32P labelled in vivo [16 -191 correspond to the proteins phosphorylated in vitro with . Two of them were identified as L44 and L45 [18, 19, 211 and are phosphorylated in vitro by the casein kinase type I1 [21, 221. Studies on the physiological role of the phosphorylation of ribosomal acidic proteins have been in progress for 10 years [23] and involved the yeast system. As shown in Ballesta's laboratory, the phosphorylation of L44, L44 and L45 might control the binding process of those proteins to ribosom...

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Section: Discussionsupporting

confidence: 77%

Specfic protein kinase from Saccharomyces cerevisiae cells phosphorylating 60S ribosomal proteins

Pilecki

Grankowski

Jacobs

et al. 1992

European Journal of Biochemistry

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“…In maize and yeast, a set of very acidic ribosomal proteins (P-proteins) that are associated with 60S ribosomal subunits are heterogeneous (62,63). In yeast, ribosomes from stationary phase are deficient in P-proteins when compared with those from exponentially growing cells (63). By using cell-free lysates, it was demonstrated that yeast ribosomes lacking P-proteins translated particular mRNAs differentially as compared with ribosomes containing P-proteins (64).…”

Section: Potential Effects Of Ribosome Heterogeneity On the Filtermentioning

confidence: 99%

Section: Potential Effects Of Ribosome Heterogeneity On the Filtermentioning

confidence: 99%

The ribosome filter hypothesis

Mauro

Edelman²

2002

Proc. Natl. Acad. Sci. U.S.A.

228

199

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A variety of posttranscriptional mechanisms affects the processing, subcellular localization, and translation of messenger RNAs (mRNAs). Translational control appears to occur primarily at the initiation rather than the elongation stage. It has been suggested that translation is mediated largely by means of a cap-binding͞ scanning mechanism. On the basis of recent findings, we propose here that differential binding of particular mRNAs to eukaryotic 40S ribosomal subunits before translation may also selectively affect rates of polypeptide chain production. In this view, ribosomal subunits themselves are considered to be regulatory elements or filters that mediate interactions between particular mRNAs and components of the translation machinery. Differences in these interactions affect how efficiently individual mRNAs compete for ribosomal subunits. These competitive interactions would depend in part on the complementarity between sequences in mRNA and rRNA, as well as on structural differences among ribosomes in different cell types. By these means, translation may either be enhanced through increased recruitment of ribosomes or inhibited through strong interactions that sequester mRNAs. We propose that ribosomal filters may be important in cell differentiation and describe experimental tests for the filter hypothesis.

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“…P1A interacts with P2B, whereas P1B interacts with P2A . However, no precise function for yeast P1 and P2 variants in ribosome is known, although the stalk content in P-protein variants depends on yeast cultural conditions (Saenz-Robles et al, 1990). Three small P-proteins (P1, P2 and P3) can be found in plants (Szick et al, 1998).…”

Section: The Stalk Proteins Among the Biological Kingdomsmentioning

confidence: 99%

The puzzling lateral flexible stalk of the ribosome

Gonzalo

Reboud

2003

Biology of the Cell

127

131

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The lateral flexible stalk of the large ribosomal subunit is made of several interacting proteins anchored to a conserved region of the 28S (26S) rRNA termed the GTPase-associated domain or thiostrepton loop. This structure is demonstrated to adopt puzzling changes of conformation following the different steps of the elongation cycle. Some of these proteins termed the P-proteins in eukaryotes and L10 and L7/L12 in bacteria, present little structural similarities between Eubacteria on one side and Archae and Eukaryotes on the other side. However, up to now, these proteins seem to present a similar macromolecular organisation and they have been involved in the same functions. Convincing evidence attests that these proteins participate in elongation factor binding to the ribosome, and it has been suggested that these proteins might be evolved in a GTP hydrolysis activating protein activity. Involvement of these proteins in the translational mechanism is discussed. Moreover, in eukaryotes, small P-proteins are also found as isolated proteins in a cytoplasmic pool that exchanges with the ribosome-associated P-proteins. Moreover, a part of the ribosomal proteins is phosphorylated (hence their P-protein names). The biological signification of these particularities is discussed.

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The acidic ribosomal proteins as regulators of the eukaryotic ribosomal activity

Cited by 84 publications

References 20 publications

Specfic protein kinase from Saccharomyces cerevisiae cells phosphorylating 60S ribosomal proteins

Specfic protein kinase from Saccharomyces cerevisiae cells phosphorylating 60S ribosomal proteins

The ribosome filter hypothesis

The puzzling lateral flexible stalk of the ribosome

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