ms2i6A deficiency enhances proofreading in translation.

The hypermodified base 2-methylthio-N6-isopentenyladenosine (ms2i6A) at position 37 occurs frequently in tRNAs that read codons starting with uridine. Here we have studied how ms2i6A affects the accuracy of poly(U) translation in vitro. Deficiency leads to a higher rejection rate of tRNA4(Leu) by more aggressive proofreading on the wild-type ribosome, but with the initial selection step unchanged. Our data indicate that ms2i6A has no effect on codon-anticodon interactions on wild-type ribosomes as long as aminoacyl-tRNA is in ternary complex with EF-Tu and GTP. ms2i6A deficiency in the cognate poly(U) reader tRNA(Phe) leads to increased misreading when the near-cognate competitor tRNA4(Leu) is wild-type. ms2i6A deficiency in tRNA4(Leu) gives a decreased error level in competition with wild-type tRNA(Phe).     

Influence of temperature and salinity on carbon and nitrogen content in Dunaliella viridis teodoresco under nitrogen sufficiency

Cell carbon and nitrogen in D. viridis are strongly dependent on the culturing conditions. Both elements increase with increasing salinity. At 31°C cell carbon is maximum and cell nitrogen minimum. This temperature was described previously (Jiménez, C., Niell, F. X. & Fernandez, J. A. (1990). Hydrobiologia, 197, 165-72) as the optimal one for achieving the maximum oxygen evolution. These results point out a possible competence for the reducing power during carbon and nitrogen assimilation processes, and under conditions of high photosynthesis (carbon assimilation) there is a partial inhibition of nitrate reduction, making C:N ratio maximum under conditions of maximum net photosynthesis.The study of cell glycerol, nitrate, structural proteins and free amino acids indicates that all of these solutes accumulate in the cells as a result of the high salinity adaptation.     

Fibroblastlike primary cells from human colon adenocarcinoma explants: Collagen biosynthesis

Summary Fibroblastlike primary cells have been obtained from human colon adenocarcinoma explants. Such cells disappear during cell culture and thus have not been previously studied. These cells have a number of altered phenotypic characteristics: a) morphology; b) growth behavior and adherence to culture substrate (they required 3 h for 90% attachment and only presented a flattened morphology 40 h after platting); and c) collagen metabolism. Increased protein biosynthesis (about double than control colon-derived fibroblasts) and maintained ability for collagen biosynthesis have been observed for the tumor-associated fibroblastlike cells. Thus, the collagen to noncollagenous proteins ratio was decreased for these cells. They exhibited an altered type I:type III collagen (5:1 instead of 3:1 in colon fibroblasts) and procollagen (2:1 against 5:1 in colon fibroblasts) ratios as well as a decreased secretion of collagen with an abnormal deposition of procollagens in the cell layer. These studies show a permanent phenotypic alteration in the tumor-associated fibroblastlike cells.     

Diurnal periodicity in Daphnia reproduction

The diurnal periodicity of reproduction in a reservoir population of Daphnia galeata Sars was tested by two methods (egg age distribution analyses and direct observation of hatching). No significant diurnal synchronization of reproduction in the natural cladoceran population was found. A conspicuous shortage of older embryonic stages was parallely revealed by analyses of diurnal changes of egg age distribution. Suggested selective feeding of fish on gravid females of Daphnia brooding embryos with black eye pigmentation is discussed.     

Rat erythrocyte glycophorins can be isolated by the lithium diiodosalicylate method used for other glycophorins.

1. The lithium diiodosalicylate/phenol method, widely employed for the isolation of membrane sialoglycoproteins (glycophorins) from mammalian erythrocytes, was applied for the first time to the purification of homologous glycoproteins from rat erythrocyte membranes. 2. The resulting preparations showed to be composed of four components, fractionated on SDS-PAGE. All four were positive for periodic acid-Schiff's reagent stain, the two largest of them being major. 3. Isolated rat glycophorins accounted for 60% of the ghost sialic acid and 1.5% of their protein. The presence of O-acetyl groups was confirmed in one-third of the sialic acid residues. 4. The molecular masses of the four glycophorin components were determined by a method which takes into account the anomalous mobility of glycoproteins on SDS-electrophoresis. Estimated values thus obtained for the actual molecular masses were 74, 32, 25 and 17 kDa.     

In vitro studies on the growth of Shigella sonnei by Lactobacillus casei and Lact. acidophilus.

The inhibitory effect of lactobacilli on growth of Shigella sonnei was studied. The effect was not due to pH alone, as addition of hydrochloric, lactic or acetic acids to culture media did not inhibit the normal growth of the shigellas. The degree of inhibition was measured by disc assay and showed that the inhibitory substance(s) can be extracellular and diffusible, varying the degrees of inhibition depending on the media tested. When broth was inoculated with mixed cultures of Lactobacillus and Shigella strains, the inhibition began at 6 h and the death phase at 9 h. The higher inhibition was produced by the mixture of lactobacilli (35.5 +/- 2.5% at 6 h culture, 57.4 +/- 1.9% at 9 h and 91.2 +/- 1.2% at 14 h). The degree of inhibition was higher when the relationship pathogen : lactobacilli was 1:10(3). The specific growth rate of lactobacilli and shigella was different in pure or mixed cultures. When the lactobacillus alone was grown for 12 h and the shigellas then added, the numbers of shigellas began to decrease immediately at 37 degrees C. This work shows that the Lactobacillus strains employed in fermented milk can be used to inhibit the growth of Sh. sonnei.     

Substrate specificity and properties of the aryl-alcohol oxidase from the ligninolytic fungus Pleurotus eryngii.

The production in a 5-1 fermenter of the extracellular enzymes laccase and aryl-alcohol oxidase by the fungus Pleurotus eryngii was studied. The latter enzyme has been purified 50-fold by Sephacryl S-200 and Mono Q chromatography. Purified aryl-alcohol oxidase is a unique flavoprotein with 15% carbohydrate content, a molecular mass of 72.6 kDa (SDS/PAGE) and a pI of 3.9. The enzyme presents wide specificity, showing activity on benzyl, cinnamyl, naphthyl and aliphatic unsaturated alcohols. Neither activity nor inhibition of veratryl alcohol oxidation was found with saturated alcohols, but competitive inhibition was produced by aromatic compounds which were not aryl-alcohol oxidase substrates, such as phenol or 3-phenyl-1-propanol. From these results, it was apparent that a double bond conjugated with a primary alcohol is necessary for substrate recognition by aryl-alcohol oxidase, and that activity is increased by the presence of additional conjugated double bonds and electron donor groups. Both affinity and maximal velocity during enzymic oxidation of methoxybenzyl alcohols were affected in a similar way by ring substituents, increasing from benzyl alcohol (Km = 0.84 mM, Vmax = 52 U/mg) to 4-methoxybenzyl alcohol (Km = 0.04 mM, Vmax = 208 U/mg). Aryl-alcohol oxidase presents also a low oxidase activity with aromatic aldehydes, but the highest activity was found in the presence of electron-withdrawing groups.     

Biochemical ethanol effects affected by a non-steroidal anti-inflammatory drug.

The non-steroidal anti-inflammatory drug, piroxicam, prevents the hepatic increase of triacylglycerols and malondialdehyde resulting from the acute intoxication of rats with ethanol. In addition, in the intoxicated rats, piroxicam consistently produces a decrease in the levels of blood ethanol in comparison with control animals. It is suggested that the anti-inflammatory compound stimulates ethanol oxidation.     

Use of whey for production of exocellular polysaccharide by a mutant strain ofXanthomonas campestris

Growth and kinetics of the production of exocellular polysaccharide was studied in a mutant strain ofXanthomonas campestris lac ⁺ during cultivation in a submerged culture in a medium containing whey. The maximum production of the polymer was observed at the initial stage of the stationary growth phase of the culture. The mean production yield was about 1.4%. The results were comparable with those obtained during cultivation on a lactose medium. Translated by Č. Novotny     

Nucleotide sequence and deduced functions of a set of cotranscribed genes of Streptomyces coelicolor A3(2) including the polyketide synthase for the antibiotic actinorhodin.

A 5.3-kb region of the Streptomyces coelicolor actinorhodin gene cluster, including the genes for polyketide biosynthesis, was sequenced. Six identified open reading frames (ORF1-6) were related to genetically characterized mutations of classes actI, VII, IV, and VB by complementation analysis. ORF1-6 run divergently from the adjacent actIII gene, which encodes the polyketide synthase (PKS) ketoreductase, and appear to form an operon. The deduced gene products of ORF1-3 are similar to fatty acid synthases (FAS) of different organisms and PKS genes from other polyketide producers. The predicted ORF5 gene product is similar to type II beta-lactamases of Bacillus cereus and Bacteroides fragilis. The ORF6 product does not resemble other known proteins. Combining the genetical, biochemical, and similarity data, the potential activities of the products of the six genes can be postulated as: 1) condensing enzyme/acyl transferase (ORF1 + ORF2); 2) acyl carrier protein (ORF3); 3) putative cyclase/dehydrase (ORF4); 4) dehydrase (ORF5); and 5) "dimerase" (ORF6). The data show that the actinorhodin PKS consists of discrete monofunctional components, like that of the Escherichia coli (Type II) FAS, rather than the multifunctional polypeptides for the macrolide PKSs and vertebrate FASs (Type I).