Antitumour activities of levans produced by Zymomonas mobilis strains

Levans produced by four Zymomonas mobilis strains showed antitumour activity against sarcoma 180 and Ehrlich carcinoma in Swiss albino mice. Levans from two strains (ZAP and CP4) had the highest effects. NMR analysis showed that the polymers were composed only of fructose units. The results suggested that the antineoplasic effect is associated to the polysaccharide molecular weight and that a particular molecular weight range may be responsible for this effect.     

Sex differences in antipredator tail-waving displays of the diurnal yellow-headed gecko Gonatodes albogularis from tropical forests of Colombia

Many vertebrate species show display behaviors when predators are in their vicinity. Some of these displays may inform the predator of the improbability of capturing the prey (i.e., pursuit-deterrent displays) and are potentially advantageous to both predator and prey. Here we present data on a tail display performed by Gonatodes albogularis, a diurnal tropical gecko. We performed transect surveys in three habitats near Bogotá in Colombia. Geckos detected during transects were approached by the observer in a standardized way, and details of their tail-waving displays were recorded. In control recordings animals were watched from a distant site without approaching them. Results showed sexual differences in tail-waving display: when approached by the observer, males performed this behavior more frequently than females. We found no significant differences between males and females in flight-initiation distances and height above the substratum when they were initially located. Results also showed that males displayed more frequently when approached than when the simulated predator remained stationary. We interpret these results as evidence that the display functions as a pursuit-deterrent signal to potential predators. However, as some tail displays were performed in the presence of conspecifics, the display may also have a social function.     

Purification and characterization of glutathione reductase from Rhodospirillum rubrum.

Glutathione reductase (NAD(P)H:GSSG oxidoreductase EC 1.6.4.2.) was purified 1160-fold to homogeneity from the nonsulfurous purple bacteria Rhodospirillum rubrum (wild type). Specific activity of the pure preparation was 102 U/mg. The enzyme displayed a typical flavoprotein absorption spectrum with maxima at 274,365, and 459 nm and an absorbance ratio A280/A459 of 7.6. The amino acid analysis revealed an unusually high content of glycine and arginine residues. Titration of the enzyme with 5,5'-dithiobis(2-nitrobenzoic acid) showed a total of two free thiol groups per subunit, one of which is made accessible only under denaturing conditions. An isoelectric point of 5.2 was found for the native enzyme. Km values, determined at pH 7.5, were 6.1 and 90 microM for NADPH and GSSG, respectively. NADH was about 2% as active as NADPH as an electron donor. The enzyme's second choice in disulfide substrate was the mixed disulfide of coenzyme A and glutathione, for which the specific activity and Km values were 5.1 U/mg and 3.4 mM, respectively. A native molecular weight of 118,000 was found, while denaturing electrophoresis gave a value of 54,400 per subunit, thus suggesting that R. rubrum glutathione reductase exists as a dimeric protein. Other physicochemical constants of the enzyme, such as Stokes radius (4.2 nm) and sedimentation coefficient (5.71 S), were also consistent with a particle of 110,000.     

A tomato cDNA inducible by salt stress and abscisic acid: nucleotide sequence and expression pattern

We have characterized a new tomato cDNA, TAS14, inducible by salt stress and abscisic acid (ABA). Its nucleotide sequence predicts an open reading frame coding for a highly hydrophilic and glycine-rich (23.8%) protein of 130 amino acids. Southern blot analysis of tomato DNA suggests that there is one TAS14 structural gene per haploid genome. TAS14 mRNA accumulates in tomato seedlings upon treatment with NaCl, ABA or mannitol. It is also induced in roots, stems and leaves of hydroponically grown tomato plants treated with NaCl or ABA. TAS14 mRNA is not induced by other stress conditions such as cold and wounding. The sequence of the predicted TAS14 protein shows four structural domains similar to the rice RAB21, cotton LEA D11 and barley and maize dehydrin genes.     

Variation in the ribosomal internal transcribed spacers (ITS1 and ITS2) among eight taxa of the Mimulus guttatus species complex

The internal transcribed spacer region (ITS1 and ITS2) of the 18S-25S nuclear ribosomal DNA sequence and the intervening 5.8S region were sequenced from three individuals in each of eight taxa of the Mimulus guttatus species complex. Three discrete variants, or "types," of ITS sequences were found, among which 30%-40% of sites differed, compared with 1%-2% within types. Dot plots indicate that these types were not related by conspicuous rearrangements or inversions. More than one ITS type was often found in the same taxon, and two of three ITS types span species boundaries, indicating their presence prior to speciation. These ITS sequences showed essentially no positional homology with the nearest sequenced relative, tomato. In contrast, the 5.8S region was relatively unvaried, with 8 of 162 sites varied in the sample among all eight taxa. The phylogeny inferred by the most common ITS sequence type, rooted by the two other ITS types, agreed with isozymes in showing the distinctness of M. nudatus, M. laciniatus, and M. tilingii from the other five taxa.      

Variation in heat shock proteins within tropical and desert species of poeciliid fishes

The 70-kilodalton heat shock protein (hsp70) family of molecular chaperones, which contains both stress-inducible and normally abundant constitutive members, is highly conserved across distantly related taxa. Analysis of this protein family in individuals from an outbred population of tropical topminnows, Poeciliopsis gracilis, showed that while constitutive hsp70 family members showed no variation in protein isoforms, inducibly synthesized hsp70 was polymorphic. Several species of Poeciliopsis adapted to desert environments exhibited lower levels of inducible hsp70 polymorphism than the tropical species, but constitutive forms were identical to those in P. gracilis, as they were in the confamilial species Gambusia affinis. These differences suggest that inducible and constitutive members of this family are under different evolutionary constraints and may indicate differences in their function within the cell. Also, northern desert species of Poeciliopsis synthesize a subset of the inducible hsp70 isoforms seen in tropical species. This distribution supports the theory that ancestral tropical fish migrated northward and colonized desert streams; the subsequent decrease in variation of inducible hsp70 may have been due to genetic drift or a consequence of adaptation to the desert environment. Higher levels of variability were found when the 30- kilodalton heat shock protein (hsp30) family was analyzed within different strains of two desert species of Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In both cases the distribution of hsp30 isoform diversity was similar to that seen previously with allozyme polymorphisms.      

The use of a cyanine dye in measuring membrane potential in yeast

An attempt was made to use 3,3'-dipropylthiacarbocyanine as a membrane potential probe in yeast by following both its fluorescence changes and its uptake by the cells under different conditions. It was found that the uptake of the dye into the cytoplasmic compartment was translated into an increased fluorescence, and the uptake by the mitochondria produced a quenching of the fluorescence. The experiments to measure uptake showed that a large amount of the dye was taken up by the cells under "deenergized" conditions. The uptake of the cyanine, however, was significantly reduced by the omission of the substrate, by deenergization of the mitochondria, or by the addition of K+, but not by Na+. This cyanine seems to be a good, qualitative indicator of the potential of the plasma membrane and of the mitochondria of the cells, with a faster response than those probes used before in yeast.