Adaptation of in vitro rat brain protein synthesis to long-term ingestion of n-butanol

Cusativin, a new cytidine-specific ribonuclease accumulated in seeds of Cucumis sativus L

Dry seeds of Cucumis sativus L. were found to contain a heat-sensitive endoribonuclease of a novel type which we have named cusativin. It was purified to apparent electrophoretic homogeneity by chromatography through S-Sepharose Fast Flow, Sephadex G-75, CM-Sepharose, Superdex 75-FPLC (fast protein liquid chromatography) and Mono S-FPLC. It is a single unglycosylated polypeptide chain with an apparent molecular mass (M(r)) of 22900. Polyclonal anti-cusativin antibodies raised in rabbits only reacted with melonin, the translation inhibitor from Cucumis melo L. Functional, Western blot and enzyme-linked immunosorbent assay (ELISA) analyses indicated that cusativin is present in the coat and cotyledons of dry seeds, but not in embryonic axes. Cusativin is accumulated in maturing seeds. By contrast, after seed germination there is degradation of the cusativin present in cotyledons but not that present in the seed coat. The preference of cusativin for polynucleotide cleavage was poly(C) >> poly(A) acids, poly(U) and poly(G) being unaffected by cusativin. Under the denaturing conditions used for RNA sequencing, cusativin acted only on poly(C). Cusativin proved to be useful for RNA sequencing, in particular, complementing the data obtained with RNase CL3. Cusativin represents a new class of plant RNase and, as far as we are aware, is the first plant enzyme that shows cleavage specificity for cytidine under the denaturing conditions of RNA sequencing.

Isolation and partial characterization of nigrin b, a non-toxic novel type 2 ribosome-inactivating protein from the bark of Sambucus nigra L

The bark of Sambucus nigra L. contains a non-toxic novel type 2 ribosome-inactivating protein that we named nigrin b. In vitro, nigrin b strongly inhibited mammalian protein synthesis but did not affect plant nor bacterial protein synthesis. The protein (M(r) 58,000) contains two subunits, A (M(r) 26,000) and B (M(r) 32,000); linked by disulphide bridge(s). Nigrin b was found to be an rRNA N-glycosidase of the rRNA of intact mammalian ribosomes and shares a very good N-terminal amino-acid sequence homology with the anti-HIV-1 proteins TAP 29 and trichosanthin.

A Cucumis sativus cell-free translation system: preparation, optimization and sensitivity to some antibiotics and ribosome inactivating proteins

A cell-free translation system was prepared from 3- to 5-day-old embryonic axes of gherkin (Cucumis sativus L.). The system was optimized for Mg²⁺ , K⁺ , NH⁺₄ , high speed supernatants, tRNA mixture from wheat germ, time and temperature. The system translates efficiently both endogenous mRNA (using a 30000 g supernatant) and polyuridylic acid (using either a 30000 g supernatant or a 100000 g supernatant supplemented with purified ribosomes). Translation by gherkin ribosomes was inhibited by several well-known eukaryotic inhibitors, antibiotics and ribosome-inactivating proteins. A translational inhibitory activity found in Cucumis sativus L. dry seeds acted on polypeptide synthesis carried out by cell-free systems from several mammals and plants, including gherkin embryonic axes. Our results indicate that the inhibitor is located in the seed bark and cotyledons, and is either blocked or absent in the embryonic axes, thus allowing the isolation of active gherkin ribosomes. The presence of the putative inhibitor appeared to be unevenly distributed in developing plants.

Changes in sensitivity of in vitro rat brain protein synthesis to the acute action of ethanol and isopropanol as a consequence of the long-term ingestion of isopropanol

Long-term treatment of rats with isopropanol in the drinking water results in a change or process of adaptation occurring in in vitro brain protein synthesis which increases the resistance of the ribosomal machinery to the acute effect of either ethanol or isopropanol. Such an increase was observed both in the system coded by endogenous messenger and in the system coded by polyuridylic acid. In both translation systems, the adaptation seems to affect the ribosomal step of polypeptide chain elongation. The increase in resistance to the alkanols apparently did not affect the inhibitory action of puromycin, fusidic acid and cycloheximide on the ribosome.