The cytogenetic systems of grasshoppers and locusts

The three endemic species of the Australian genusTolgadia are all distributed in the northern tropical and subtropical areas. They are distinguishable both on morphological and cytological grounds. All three have a derived neo XY, neo XX sex chromosome system involving distinct elements of a basically 11-membered autosome set, namely (spacies-1) (bivittata) and (infirma). Additionallybivittata is homozygous for two autosomal fusions involving and giving 2n=18 as compared to the complement of 2n=22 present in the other two species. Two of the species,bivittata and species-1, have a comparable mean cell chiasma frequency despite their difference in chromosome number. That ofinfirma is significantly higher. Coupled with this, some of the populations ofinfirma are polymorphic for supernumerary heterochromatic segments, principally on the smallest autosome. Such segments increase the mean cell chiasma frequency still further. Thusinfirma, which is the least habitat restricted despite its brachypterous nature, not only has the highest mean cell chiasma frequency but, in addition, has at its disposal a polymorphism capable of magnifying this difference.     

Coumarin glycosides of seseli montanum

Three new coumarin glycosides isolated from roots of Seseli montanum were shown to be the 3′-O-,2′-O-, and the 7-O-β-D-glucopyranosides respectively of 2′(R)-6-(2′,3′-dihydroxy-3′-methylbutyl)-7-hydroxy-coumarin. The structures were elucidated by spectroscopic and chemical methods. (R)-Configuration was assigned to the aglycone, also known as ( + )-peucedanol, and to its 7-methyl ether, ( + )-ulopterol, by chemical correlation. Additionally, apterin was obtained and characterized.     

CELL DIVISION IN THE FILAMENTOUS PLEURASTRUM AND ITS COMPARISON WITH THE UNICELLULAR PLATYMONAS (CHLOROPHYCEAE)1

At prophase in Pleurastrum, extranuclear spindle microtubules develop from the region of centrioles, which lie lateral to the nucleus midway between the future sites of the metaphase spindle poles. The microtubules then move laterally to overarch the nucleus and finally become incorporated into the spindle. The centrioles do not migrate and therefore lie in the same plane as the chromosomes at metaphase. At telophase, 2, more different systems of microtubules develop from the vicinity of the centrioles—a phycoplast and extensive arrays of microtubules that ensheath the daughter nuclei. Cell division in the filamentous Pleurastrum is compared to that in the green flagellate, Platymonas. The similarities between cell division in the 2 algae are interpreted as evidence: (i) that rhizoplasts (which in Platymonas resemble myofibrils) are somehow homologous to microtubules; and, (ii) that cell division in Pleurastrum differs from cell division in other examined filamentous chlorophycean genera because Pleurastrum has an independent evolutionary origin from a monad with Platymonas-like characteristics.     

Arabidopsis consensus intron sequences

We have analysed 998 Arabidopsis intron sequences in the EMBL database. All Arabidopsis introns to adhere to the :GU...AG: rule with the exception of 1% of introns with :GC at their 5 ends. Virtually all of the introns contained a putative branchpoint sequence (YUNAN) 18 to 60 nt upstream of the 3 splice site. Although a polypyrimidine tract was much less apparent than in vertebrate introns, the most common nucleotide in the region upstream of the 3 splice site was uridine. Consensus sequences for 5 and 3 splice sites and branchpoint sequences for Arabidopsis introns are presented.     

Mutational variants of the Neurospora crassa NADP-specific glutamate dehydrogenase altered in a conformational equilibrium

Seven defective variants of the NADP-specific glutamate dehydrogenase of Neurospora crassa, resulting from missense mutations in the am gene, are quantitatively different from the wild type enzyme in the allosteric equilibrium between enzymically active A and inactive I conformations, and in the kinetics of conformational transitions between these states. These abnormalities have been defined using measurements of enzymic activity and of the intrinsic tryptophan fluorescence emission of the proteins.The protein from am¹(Ser336 → Phe) is hyperstable in the A conformation but this state is enzymically inactive because it fails to bind coenzyme. The other six variants are potentially active but are, to different extents, hyperstable in the I conformation. They form a series of analogues, those of am¹³¹ (substitution not determined), am¹³⁰(Pro75 → Ser), am³(Glu393 → Gly), am²(His142 → Gln), am¹⁹(Lys141 → Met) in order of increasing abnormality of the equilibrium position. am¹²²(Trp389 changed to an undetermined residue) resembles am¹⁹. The hyperstability is sufficient to explain the auxotrophy of am The proteins of am¹³¹ and am¹³⁰ are, in addition, abnormally prone to denaturation. These hyperstabilities of the I state are small in free energy terms, consistent with the fact that the defects of some variants may be corrected or partially corrected by second site substitutions or by complementation in hybrid hexamers with am¹ protein.Five out of seven amino acid substitutions known to affect this equilibrium (including Gln391 → Arg of revertant am¹⁹24) involve charged residues clustered around positions 141 and 391. Interactions between these two parts of the polypeptide are implicated in stabilizing the A state of the enzyme, possibly by providing protonatable groups or part of the dicarboxylate binding site, and in affecting the environment of a tryptophan residue responsible for the fluorescence difference of the two conformations.     

Chronic hypoxia alters the function of NOS nerves in cerebral arteries of near-term fetal and adult sheep.

In addition to adrenergic innervation, cerebral arteries also contain neuronal nitric oxide synthase (nNOS)-expressing nerves that augment adrenergic nerve function. We examined the impact of development and chronic high-altitude hypoxia (3,820 m) on nNOS nerve function in near-term fetal and adult sheep middle cerebral arteries (MCA). Electrical stimulation-evoked release of norepinephrine (NE) was measured with HPLC and electrochemical detection, whereas nitric oxide (NO) release was measured by chemiluminescence. An inhibitor of NO synthase, N(omega)-nitro-l-arginine methyl ester (l-NAME), significantly inhibited stimulation-evoked NE release in MCA from normoxic fetal and adult sheep with no effect in MCA from hypoxic animals. Addition of the NO donor S-nitroso-N-acetyl-dl-penicillamine fully reversed the effect of l-NAME in MCA from normoxic animals with no effect in MCA from hypoxic animals. Electrical stimulation caused a significant increase in NO release in MCA from normoxic animals, an effect that was blocked by the neurotoxin tetrodotoxin, whereas there was no increase in NO release in MCA from hypoxic animals. Relative abundance of nNOS as measured by Western blot analysis was similar in normoxic fetal and adult MCA. However, after hypoxic acclimitization, nNOS levels dramatically declined in both fetal and adult MCA. These data suggest that the function of nNOS nerves declines during chronic high-altitude hypoxia, a functional change that may be related to a decline in nNOS protein levels.     

Validation of measurements of ventilation-to-perfusion ratio inequality in the lung from expired gas.

The analysis of the gas in a single expirate has long been used to estimate the degree of ventilation-perfusion (Va/Q) inequality in the lung. To further validate this estimate, we examined three measures of Va/Q inhomogeneity calculated from a single full exhalation in nine anesthetized mongrel dogs under control conditions and after exposure to aerosolized methacholine. These measurements were then compared with arterial blood gases and with measurements of Va/Q inhomogeneity obtained using the multiple inert gas elimination technique. The slope of the instantaneous respiratory exchange ratio (R slope) vs. expired volume was poorly correlated with independent measures, probably because of the curvilinear nature of the relationship due to continuing gas exchange. When R was converted to the intrabreath Va/Q (iV/Q), the best index was the slope of iV/Q vs. volume over phase III (iV/Q slope). This was strongly correlated with independent measures, especially those relating to inhomogeneity of perfusion. The correlations for iV/Q slope and R slope considerably improved when only the first half of phase III was considered. We conclude that a useful noninvasive measurement of Va/Q inhomogeneity can be derived from the intrabreath respiratory exchange ratio.     

Topoisomerase III can serve as the cellular decatenase in Escherichia coli

topB, encoding topoisomerase III, was identified as a high copy suppressor of the temperature-sensitive parC1215 allele, encoding one of the subunits of topoisomerase IV. Overexpression of topoisomerase III at the nonpermissive temperature was shown subsequently to restore timely chromosome decatenation and suppress lethality in strains carrying either temperature-sensitive parE or parC alleles. By developing an assay in vitro for precatenane unlinking, we demonstrated directly that both topoisomerase III and topoisomerase IV were efficient at this task, whereas DNA gyrase was very inefficient at precatenane removal. These observations suggest that precatenane unlinking is sufficient to sustain decatenation of replicating daughter chromosomes in the cell.