Cis-acting elements stimulating kinetoplastid guide RNA-directed editing

The coding sequence of several mitochondrial mRNAs of the kinetoplastid protozoa is created through the insertion and deletion of specific uridylates. The editing reactions are required to be highly specific in order to ensure that functional open reading frames are created in edited mRNAs and that potentially deleterious modification of normally nonedited sequence does not occur. Selection-amplification and mutagenesis were previously used to identify the optimal sequence requirements for in vitro editing. There is, however, a minority of natural editing sites with suboptimal sequence. Several cis-acting elements, obtained from an in vitro selection, are described here that are able to compensate for a suboptimal editing site. An A + U sequence element within the 5'-untranslated region of cytochrome b mRNA from Leishmania tarentolae is also demonstrated to function as a cis-acting guide RNA and is postulated to compensate for a suboptimal editing site in vivo. Two proteins within an enriched editing extract are UV-cross-linked to two different in vitro selected editing substrates more efficiently than poorly edited RNAs. The results suggest that these proteins contribute to the specificity of the editing reaction.     

Computer modeling of the human systemic arterial tree

A model of the human systemic arterial tree has been devised, based on a lumped-parameter-circuit approximate form. This model has been set up and studied on an analog computer. A feature of this simulation is the division of the arterial system into sections whose lengths are inversely proportional (approximately) to their cross-sectional area-or what is termed ‘equal-volume’ modeling.

Great care was exercised in the determination of the model parameters, using expressions for these parameters from a recent paper by Rideout and Dick on fluid flow in distensible tubes, with numerical values based on measurements reported in the medical literature.

The simulated pressure and flow waveforms obtained with the model compare favorably with data recorded from the normal adult human, and exhibit such well-known features as distal delay and peaking of pressure pulses. The aortic input impedance vs. frequency curve checks well against measurements on the human. The model also provides a simple means for determination of cardiac output, cardiac work and cardiac power under various assumed conditions such as variation of heart rate.     

Structural studies of water-soluble glycoproteins from Cannabis sativa L

Two carbohydrate-protein fractions, isolated from Cannabis sativa L. by extraction with water and chromatography on DEAE-cellulose, contained arabinose, galactose, glucose, mannose, galacturonic acid, 2-acetamido-2-deoxyglucose, and 2-acetamido-2-deoxygalactose. The structure of the carbohydrate moieties was investigated by methylation analysis and Smith degradation. A high percentage of end-groups indicates a large degree of branching, glucose and galactose being the main branch-points, linked at C-3 and C-6. The hexoses are also present as unbranched residues in the chain, largely as (1→3)- and (1→4)-linked units and as end-groups. Arabinofuranosyl units constitute the main part of the non-reducing end-groups, and are also present as part of the chain. The polysaccharide chains are probably linked to protein through the hydroxyl group of hydroxyproline.     

Water-soluble glycoproteins from Cannabis sativa (Thailand)

Glycoproteins were extracted with water from leaves of Cannabis sativa grown from seeds of Thailand origin. By ion exchange chromatography the material was separated into a neutral and an acidic fraction. Both glycoprotein fractions contained arabinose, galactose, glucose, mannose and xylose, and in addition rhamnose and galacturonic acid were present in the acidic fraction. The carbohydrate moieties were investigated by methylation analysis and Smith-degradation, whereas the glycopeptide linkage was studied by alkaline hydrolysis in the presence of NaBH₄ and Na₂SO₃, respectively. This linkage was shown to be of the serine-O-galactoside type. The carbohydrate structure is highly branched, the majority of branches terminating in arabinofuranose end groups. Arabinose is also present in the chain, predominantly (1 → 4)- and/or (1 → 5)-linked. Galactose makes up most of the main chain as (1 → 3)-linked residues but also constitutes end groups and branch points, as do mannose and/or glucose. Xylose and rhamnose are present as (1 → 4)- and (1 → 2)-linked units, respectively. Galacturonic acid is assumed to be (1 → 4)- linked with some branching at 3 position. The amino acid hydroxyproline, present in the glycoprotein of South African Cannabis leaves, was absent in the corresponding Thailand material.     

Glycoproteins of the opium poppy

Two carbohydrate-protein fractions were isolated from the water-soluble biopolymer from opium poppy capsules by chromatography on SP-Sephadex. The carbohydrate chains are composed of arabinose, rhamnose, xylose, mannose, glucose, galactose, galacturonic acid, glucuronic acid and 4-O-methyl glucuronic acid. Methylation analysis indicated a high degree of branching suggesting a very complex structure. Treatment of the glycoprotein with NaOH in the presence of NaBH₄ resulted in a significant decrease in the serine and threonine content. The carbohydrate side chains released contained the sugar alcohol, galactitol. These results indicate that polysaccharide chains are linked to protein via serine-O-galactoside linkages.     

Water-soluble glycoproteins from Cannabis sativa (South Africa)

The water-soluble glycoproteins obtained from Cannabis leaves of plants grown from South African seeds have been further studied. Treatment of the glycoprotein fractions with NaOH in the presence of NaBH₄, resulted in a significant decrease in the serine content and a corresponding increase in alanine. The carbohydrate side chains released contained the sugar alcohol, galactitol. By treatment of the glycoprotein fractions with NaOH in the presence of Na₂SO₃, and subsequent acid hydrolysis, cysteic acid was formed. These data indicate that carbohydrate and protein are connected via serine-O-galactoside linkages. Further investigation of the structure of the carbohydrate part of the glycoproteins was carried out by methylation analysis, Smith-degradation and enzyme incubation. The present glycoprotein material of plants grown from South African seeds is similar to the material previously investigated, but in contrast to the latter, it is devoid of hexosamine.     

A contradictory GLABRA3 allele helps define gene interactions controlling trichome development in Arabidopsis

Previously characterized Arabidopsis gl3 mutants have trichomes that are smaller, less branched and undergo fewer rounds of endoreplication than wild-type trichomes. A new gl3 mutant, called gl3-sst, has oddly shaped trichomes that over expand during early development, undergo more endoreduplication and that have a striking nuclear morphology. The mutant nuclei consist of many interconnected lobes; however, only a single set of polytene-like chromosomes reside in the mutant nuclei. The predicted gl3-sst polypeptide has a Leu to Phe substitution (codon 78) within a region responsible for protein-protein interaction. Yeast interaction assays comparing GL3 with gl3-sst proteins show that the mutant protein interaction with GL1 and TTG1 is decreased by 75% and 50%, respectively, but there is no difference in its interaction with TRY. Furthermore, TRY has the ability to prevent the GL1 GL3 interaction and the GL1 gl3-sst interaction is even more sensitive to TRY. Analysis of plants expressing functional GFP-tagged versions of GL1, GL3 and TRY show that the proteins are localized in trichome nuclei. These results have been used to model trichome initiation in terms of protein interactions and threshold levels of activator complex.