Biomaterial Database

Dual effects of the ricin A chain on protein synthesis in rabbit reticulocyte lysate. Inhibition of initiation and translocation. 1990

R W Osborn, and M R Hartley

Department of Biological Sciences, University of Warwick, Coventry, England.

Ricin A chain caused inhibition of protein synthesis by reticulocyte lysate with concomitant depurination of 28S rRNA. The partial reaction(s) of protein synthesis inhibited was investigated by following the appearance of [35S]methionine from initiator [35S]Met-tRNA into 40S ribosomal subunits, 80S monosomes and polysomes. Ricin A chain caused an accumulation of [35S]Met in monosomes which did not enter polysomes. In these respects the effects of the ricin A chain resembled those of diphtheria toxin, an inhibitor of elongation-factor-2-catalyzed translocation. This is consistent with the previously proposed site of action of ricin as an inhibitor of elongation. However, the inhibitory effects of the ricin A chain and diphtheria toxin are not equivalent because we observed that the rate of formation of the 80S initiation complex was reduced approximately sixfold with the ricin A chain relative to diphtheria toxin. Analysis of methionine-containing peptides bound to 80S monosomes in ricin-A-chain-inhibited and diphtheria-toxin-inhibited lysates, programmed with globin mRNA, revealed a predominance of Met-Val, suggesting that the elongation cycle is inhibited at the translocation step. Translocation was also implicated as the step blocked in both the ricin-A-chain-inhibited and diphtheria-toxin-inhibited lysates, by the finding that nascent peptide chains were unreactive towards puromycin. It is concluded that ricin-A-chain-modified ribosomes are deficient in two protein synthesis partial reactions: the formation of the 80S initiation complex during initiation and the translocation step of the elongation cycle.

UI	MeSH Term	Description	Entries
D010442	Peptide Chain Initiation, Translational	A process of GENETIC TRANSLATION whereby the formation of a peptide chain is started. It includes assembly of the RIBOSOME components, the MESSENGER RNA coding for the polypeptide to be made, INITIATOR TRNA, and PEPTIDE INITIATION FACTORS; and placement of the first amino acid in the peptide chain. The details and components of this process are unique for prokaryotic protein biosynthesis and eukaryotic protein biosynthesis.	Chain Initiation, Peptide, Translational,Protein Biosynthesis Initiation,Protein Chain Initiation, Translational,Protein Translation Initiation,Translation Initiation, Genetic,Translation Initiation, Protein,Translational Initiation, Protein,Translational Peptide Chain Initiation,Biosynthesis Initiation, Protein,Genetic Translation Initiation,Initiation, Genetic Translation,Initiation, Protein Biosynthesis,Initiation, Protein Translation,Initiation, Protein Translational,Protein Translational Initiation
D010444	Peptide Elongation Factor Tu	A protein found in bacteria and eukaryotic mitochondria which delivers aminoacyl-tRNA's to the A site of the ribosome. The aminoacyl-tRNA is first bound to a complex of elongation factor Tu containing a molecule of bound GTP. The resulting complex is then bound to the 70S initiation complex. Simultaneously the GTP is hydrolyzed and a Tu-GDP complex is released from the 70S ribosome. The Tu-GTP complex is regenerated from the Tu-GDP complex by the Ts elongation factor and GTP.	Elongation Factor Tu,EF-Tu,Eucaryotic Elongation Factor Tu,Protein Synthesis Elongation Factor Tu,eEF-Tu,EF Tu,Factor Tu, Elongation,eEF Tu
D011687	Purines	A series of heterocyclic compounds that are variously substituted in nature and are known also as purine bases. They include ADENINE and GUANINE, constituents of nucleic acids, as well as many alkaloids such as CAFFEINE and THEOPHYLLINE. Uric acid is the metabolic end product of purine metabolism.
D011817	Rabbits	A burrowing plant-eating mammal with hind limbs that are longer than its fore limbs. It belongs to the family Leporidae of the order Lagomorpha, and in contrast to hares, possesses 22 instead of 24 pairs of chromosomes.	Belgian Hare,New Zealand Rabbit,New Zealand Rabbits,New Zealand White Rabbit,Rabbit,Rabbit, Domestic,Chinchilla Rabbits,NZW Rabbits,New Zealand White Rabbits,Oryctolagus cuniculus,Chinchilla Rabbit,Domestic Rabbit,Domestic Rabbits,Hare, Belgian,NZW Rabbit,Rabbit, Chinchilla,Rabbit, NZW,Rabbit, New Zealand,Rabbits, Chinchilla,Rabbits, Domestic,Rabbits, NZW,Rabbits, New Zealand,Zealand Rabbit, New,Zealand Rabbits, New,cuniculus, Oryctolagus
D012156	Reticulocytes	Immature ERYTHROCYTES. In humans, these are ERYTHROID CELLS that have just undergone extrusion of their CELL NUCLEUS. They still contain some organelles that gradually decrease in number as the cells mature. RIBOSOMES are last to disappear. Certain staining techniques cause components of the ribosomes to precipitate into characteristic "reticulum" (not the same as the ENDOPLASMIC RETICULUM), hence the name reticulocytes.	Reticulocyte
D002499	Centrifugation, Density Gradient	Separation of particles according to density by employing a gradient of varying densities. At equilibrium each particle settles in the gradient at a point equal to its density. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)	Centrifugations, Density Gradient,Density Gradient Centrifugation,Density Gradient Centrifugations,Gradient Centrifugation, Density,Gradient Centrifugations, Density
D002855	Chromatography, Thin Layer	Chromatography on thin layers of adsorbents rather than in columns. The adsorbent can be alumina, silica gel, silicates, charcoals, or cellulose. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)	Chromatography, Thin-Layer,Thin Layer Chromatography,Chromatographies, Thin Layer,Chromatographies, Thin-Layer,Thin Layer Chromatographies,Thin-Layer Chromatographies,Thin-Layer Chromatography
D004167	Diphtheria Toxin	An ADP-ribosylating polypeptide produced by CORYNEBACTERIUM DIPHTHERIAE that causes the signs and symptoms of DIPHTHERIA. It can be broken into two unequal domains: the smaller, catalytic A domain is the lethal moiety and contains MONO(ADP-RIBOSE) TRANSFERASES which transfers ADP RIBOSE to PEPTIDE ELONGATION FACTOR 2 thereby inhibiting protein synthesis; and the larger B domain that is needed for entry into cells.	Corynebacterium Diphtheriae Toxin,Toxin, Corynebacterium Diphtheriae
D005914	Globins	A superfamily of proteins containing the globin fold which is composed of 6-8 alpha helices arranged in a characterstic HEME enclosing structure.	Globin
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia