Elongation and Termination Reactions of Protein Synthesis on Maize Root Tip Polyribosomes Studied in a Homologous Cell-Free System

Webster, Cecelia; Kim, Chang-Yub; Roberts, Justin K. M.

doi:10.1104/pp.96.2.418

Cited by 38 publications

(32 citation statements)

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“…It was found using cytosolic extracts of Xenopus oocytes that the rates of in vitro translation at pH 7.0 and 6.8 were reduced by approximately 15% and 65%, respectively, relative to pH 7.3 (Grandin and Charbonneau, 1989). Furthermore, a strong pH dependence of protein synthesis has been shown in polyribosome preparations from maize root tips by Webster et al (1991), who suggested that the pH dependence of root-tip protein synthesis could provide a mechanism that enables the cell's translational machinery to sense changes in pH c , leading directly to selective gene expression. In mammalian cells, a role for cytosolic acidification in signaling programmed cell death is unlikely (Schrode et al, 1997), but changes in cytosolic a K have been implicated (Hughes et al, 1997).…”

Section: The Cellular Mechanism Of Growth Inhibition During K ؉ Starvmentioning

confidence: 96%

“…A decrease in cytosolic a K in expanding cells would be expected to diminish rates of protein synthesis, leading to a decrease in the rates of root elongation and dry matter production White, 1993). Changes in pH c have been shown to alter the rate of protein synthesis in both animal (Grandin and Charbonneau, 1989) and plant cells (Webster et al, 1991). To test this hypothesis, pH c and protein synthesis were measured in root tips treated with butyrate or procaine to alter pH c in seedlings growing under K ϩ -starved or K ϩ -replete conditions.…”

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confidence: 99%

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The Role of Cytosolic Potassium and pH in the Growth of Barley Roots

1998

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Section: The Cellular Mechanism Of Growth Inhibition During K ؉ Starvmentioning

confidence: 96%

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confidence: 99%

The Role of Cytosolic Potassium and pH in the Growth of Barley Roots

1998

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“…The effect of RlPs on translation of endogenous (maize polyribosomal) mRNAs or BMV mRNA (added at 5 pglmL) was then assayed by measuring incorporation of 3H-leucine into protein at 30 min, as previously described (Webster et al, 1991). Micrococcal nucleasetreated wheat germ and rabbit reticulocyte lysates and BMV RNA were from Promega.…”

Section: Ttanslation Lnhibition Assaysmentioning

confidence: 99%

A maize ribosome-inactivating protein is controlled by the transcriptional activator Opaque-2.

et al. 1992

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Although synthesis of the cytosolic maize albumin b-32 had been shown to be controlled by the Opaque-2 regulatory locus, its function was unknown. We show here that b-32 is a member of the large and widely distributed class of toxic plant proteins with ribosome-inactivating activity. These ribosome-inactivating proteins (RIPs) are RNA N-glycosidases that remove a single base from a conserved 28s rRNA loop required for elongation factor l u binding. Cell-free in vitro translation extracts were used to show that both maize and wheat ribosomes were resistant to molar excesses of b-32 but not to the dicotyledonous RIP gelonin. We extracted RIP activity from kernels during seed maturation and germination. The amount of RIP activity increased during germination, although the amount of b-32 protein remained fairly constant. Expression of a maize RIP gene under the control of an endosperm-specific transcriptional regulator may be an important clue prompting investigation of the biological basis for RIP expression in seeds of other plants. INTRODUCTIONRibosome-inactivating proteins (RIPs) are a widely distributed group of toxic plant proteins that catalytically inactivate eukaryotic ribosomes (for review, see Stirpe and Barbieri, 1986). RlPs function as N-glycosidases to remove a specific adenine in a conserved loop of the large rRNA . This irreversible modification renders the ribosome unable to bind elongation factor l a , thereby blocking translation. Because this translational inhibitory activity is toxic, RlPs have been tested extensively for use as immunotoxins and antiviral agents and more recently for their effects on protozoa, insects, and fungi (Barbieri and Stirpe, 1982;Cenini et al., 1988;Gatehouse et al., 1990;Leah et al., 1991).RIP activities have been found in the seed, root, leaf, or sap of more than 50 different plant species (Gasperi-Campani et al., 1985). Two forms of RlPs have been described (Stirpe and Barbieri, 1986). Type 1 RlPs such as pokeweed antiviral protein, trichosanthin, the barley translation inhibitor, and gelonin are monomeric enzymes, each with an approximate M, of 30,000 (Irvin, 1975;Stirpe et al., 1980;Asano et al., 1984;Maraganore et al., 1987;Yeung et al., 1988). Type 2 RlPs such as ricin, abrin, and modeccin are highly toxic heterodimeric proteins, each with an approximate M, of 60,000 in which one polypeptide with RIP activity (A-chain) is linked by a disulfide bridge to a galactose-binding lectin (B-chain; Pihl, 1973, 1982;Stirpe et al., 1978).Type 1 RlPs and the A-chain of type 2 RlPs have basic isoelectric points, and many have signal peptides that are not To whom correspondence should be addressed. present in the mature protein (Stirpe and Barbieri, 1986). Although RlPs share biological activity, they typically exhibit similarities of <50%, and antibodies raised against RlPs seldom cross-react with RlPs from distantly related species (Ready et al., 1988). The maize b-32 protein has homology with severa1 previously characterized RIPs, yet it is a singlechain acidic protein tha...

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“…We have demonstrated that oxygen deprivation results in the competitive differences between mRNAs for initiation of translation (Fennoy and Bailey-Serres, 1995;BaileySerres and Dawe, 1996). Regulation also occurs after initiation, since certain mRNAs loaded onto polyribosomes are not efficiently translated (Webster et al, 1991;Fennoy and Bailey-Serres, 1995). In yeast, ribosomes lacking P1 and P2 selectively translate a subset of cellular mRNAs, and the www.plantphysiol.org on May 12, 2018 -Published by Downloaded from Copyright © 1997 American Society of Plant Biologists.…”

Section: Oxygen Deprivation Stimulates Dynamic Alterations In the 60smentioning

confidence: 99%

Acidic Phosphoprotein Complex of the 60S Ribosomal Subunit of Maize Seedling Roots (Components and Changes in Response to Flooding)

et al. 1997

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We determined that ribosomes of seedling roots of maize (Zea mays 1.) contain the acidic phosphoproteins (P-proteins) known to form a flexible lateral stalk structure of the 60s subunit of eukaryotic ribosomes. l h e P-protein stalk, composed of PO, P1, and P2, interacts with elongation factors, mRNA, and tRNA during translation. Acidic proteins of 13 to 15.5 k D were released as a complex from ribosomes with 0.4 M NH,CI/SO% ethanol. Protein and cDNA sequence analysis confirmed that maize ribosomes contain one type of P1, two types of P2, and a fourth and novel Pl/PZ-type protein.This novel P-protein, designated P3, has the conserved C terminus of P1 and P2. P1, P2, and P3 are similar in deduced m a s (1 1.4-1 2.2 kD) and isoelectric point (4.1-4.3). A 35.5-t o 36-kD acidic protein was released at low levels from ribosomes with 1 .O M NH,C1/50% ethanol and identified as PO. Labeling of roots with [32P]inorganic phosphate confirmed the in vivo phosphorylation of the P-proteins.Flooding caused dynamic changes in the P-protein complex, which affected the potential of ribosome-associated kinases and casein kinase II t o phosphorylate the P-proteins. We discuss possible alterations of the ribosomal P-protein complex and consider that these changes may be involved in the selective translation of mRNA in flooded roots.Ribosomes are a two-subunit organelle, and are the site of mRNA translation into protein in a11 organisms. The large ribosomal subunit is a complex macromolecule that is composed of rRNAs, a large number of basic (high-pI) proteins, and a small number of acidic (low-pI) proteins. Across evolutionary kingdoms and phyla the large ribosoma1 subunit is variable in size, but possesses a number of morphological features that are universally conserved. For example, a universal feature of the peptidyl transferase region of the large subunit is a complex of acidic proteins that form the body and stalk of a lateral protuberance (Moller, 1990; Liljas, 1991).In bacteria the acidic protein stalk of the 50s ribosomal subunit is composed of ribosomal protein, L10, and two dimers of L7 and L12 in a (L7/L12),-LlO pentameric complex (Moller, 1990; Liljas, 1991). L10 is a 17-kD acidic pro- tein that interacts with the 23s rRNA scaffold of the large subunit within the GTPase domain of the rRNA. L7 and L12 are 12-kD acidic proteins that are encoded by a single gene, but differ in that the N-terminal Ser of L7 is posttranslationally aminoacetylated. The N-terminal domain of L7 and L12 forms an a-helical structure that is responsible for dimer formation and binding to M O . A central region of acidic residues forms a flexible hinge that allows the dimers to assume an elongated conformation that forms the stalk or a closed conformation in which the C-and N-terminal domains are in close proximity on the body of the 50s ribosomal subunit (Oleinikov et al., 1993;Traut et al., 1993). The C-terminal regions of L7 and L12 are required for binding of elongation factor G, and the subsequent hydrolysis of GTP that occurs in the transloca...

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Elongation and Termination Reactions of Protein Synthesis on Maize Root Tip Polyribosomes Studied in a Homologous Cell-Free System

Cited by 38 publications

References 31 publications

The Role of Cytosolic Potassium and pH in the Growth of Barley Roots

The Role of Cytosolic Potassium and pH in the Growth of Barley Roots

A maize ribosome-inactivating protein is controlled by the transcriptional activator Opaque-2.

Acidic Phosphoprotein Complex of the 60S Ribosomal Subunit of Maize Seedling Roots (Components and Changes in Response to Flooding)

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