Sequence, organization, and evolution of the A+T region of Drosophila melanogaster mitochondrial DNA

The long (4.6-kb) A+T region of Drosophila melanogaster mitochondrial DNA has been cloned and sequenced. The A+T region is organized in two large arrays of tandemly repeated DNA sequence elements, with nonrepetitive intervening and flanking sequences comprising only 22% of its length. The first repeat array consists of five repeats of 338-373 bp. The second consists of four intact 464-bp repeats and a fifth partial repeat of 137 bp. Three DNA sequence elements are found to be highly conserved in D. melanogaster and in several Drosophila species with short A+T regions. These include a 300-bp DNA sequence element that overlaps the DNA replication origin and two thymidylate stretches identified on opposite DNA strands. We conclude that the length heterogeneity observed in the A+T regulatory region in mitochondrial DNAs from the genus Drosophila results from the expansion (and contraction) of the number of repeated DNA sequence elements. We also propose that the 300-bp conserved DNA sequence element, in conjunction with another primary sequence determinant, perhaps the adjacent thymidylate stretch, functions in the regulation of mitochondrial DNA replication.      

A small heat shock protein from Leuconostoc oenos induced by multiple stresses and during stationary growth phase

In Leuconostoc oenos , a malolactic bacterium, the synthesis of a stress protein called LO18 with an apparent molecular mass of 18 kDa was greatly induced after heat (42°C), acid (pH 3) or ethanolic (12% (v/v)) shocks. Moreover, the LO18 protein synthesis was induced in stationary growth phase and was detected for a long time (30 h) during this growth phase. Significant identity was found between the N-terminal parts of the LO18 protein and the Hsp18 from Clostridium acetobutylicum suggesting that LO18 protein belongs to the family of small heat shock proteins conserved in prokaryotic and eukaryotic cells.     

The secretory nature of the lesion of carrot cell variant ts11, rescuable by endochitinase

The carrot cell variant ts11 is unable to form somatic embryos at the non-permissive temperature of 32 °C, but the block can be overcome by the addition of a 32-kDa acidic endochitinase to the medium. In this work we conducted a cyto-histological analysis of the blocked embryo forms. The morphology of the endomembrane system is altered; in particular, the ER is dilated and may show electron-dense precipitates and continuity with the plasma membrane. These morphological alterations do not occur in the presence of externally-added endochitinase. We also noticed modifications of the culture medium that are probably related to the morphological observations: the total amount of secreted proteins is reduced and pulse-chase experiments revealed that, compared with wild-type cells, the secretion of major polypeptides is reduced while new minor polypeptides are secreted. Western blot analysis revealed the presence of the binding protein BiP, a resident of the ER and of glutamine synthase, a cytosolic protein, in the medium of ts11 but not wild-type cells. These results indicate that ts11 is altered in the secretory pathway but do not clarify the role of endochitinase. Received: 13 January 1997 / Accepted: 21 March 1997     

Pseudomonas aeruginosa alkaline protease: evidence for secretion genes and study of secretion mechanism.

A 6.5-kb DNA fragment carrying the functions required for specific secretion of the extracellular alkaline protease produced by Pseudomonas aeruginosa was cloned. The whole 6.5-kb DNA fragment was transcribed in one direction and probably carried three genes involved in secretion. The expression in trans of these genes, together with the apr gene, in Escherichia coli allowed synthesis and secretion of the alkaline protease, which was extensively investigated by performing pulse-chase experiments under various conditions. We demonstrated the absence of a precursor form, as well as the independence of alkaline protease translocation from SecA. The absence of secretion genes impaired alkaline protease secretion; the protein then remained intracellular and was partially degraded.     

Cloning of the Pseudomonas aeruginosa alkaline protease gene and secretion of the protease into the medium by Escherichia coli.

Pseudomonas virulence is thought to depend on multiple characteristics, including the production of an extracellular alkaline protease. We report the isolation, from a PAO1 DNA genomic bank, of a cosmid carrying the structural gene coding for alkaline protease. By in vivo mutagenesis using transposon Tn1735, which functions as a transposable promoter, the expression of an 8.8-kilobase DNA fragment under control the tac promoter was obtained. When expressed in Escherichia coli, active alkaline protease was synthesized and secreted to the extracellular medium in the absence of cell lysis.     

Acid tolerance inLeuconostoc oenos. Isolation and characterization of an acid-resistant mutant

The acid tolerance ofLeuconostoc oenos was examined in cells surviving at pH 2.6, which is lower than the acid limit of growth (about pH 3.0). Acid-adapted cells survived better than non-adapted cells. Tolerance to acid stress was found to be dependent upon the adaptive pH. Acid resistance was increased by an order of magnitude for cultures adapted to a pH of about 2.9. Inhibiting protein synthesis with chloramphenicol prior to acid shock revealed that acid adaptation may involve two separate systems, one of which appears to be independent of protein synthesis. The acid-resistant mutant LoV8413, isolated during a long-term survival screen at pH 2.6, was found to be able to grow in acidic media and was characterized by a high H⁺-ATPase activity at low pH. The data from electrophoretic analysis of total proteins labeled with [³⁵S] methionine indicate that large amounts of a protein of 42 kDa molecular mass were produced within this acid-resistant mutant.     

Synthesis and topoisomerase poisoning activity of A-ring and E-ring substituted luotonin A derivatives

A series of A-ring and E-ring analogues of the natural product luotonin A, a known topoisomerase I poison, was evaluated for growth inhibition in human carcinoma and leukemia cell lines. Rational design of structures was based on analogues of the related alkaloid camptothecin, which has been demonstrated to exert cytotoxic effects by the same mechanism of action. When compared to luotonin A, several compounds exhibited an improved topoisomerase I-dependent growth inhibition of a human leukemia cell line.     

Influences of environmental variation on anadromous Arctic charr from the Hornaday River,NWT

Hydrobiologia - Insights from long-term subsistence fisheries data can improve our understanding of the population-specific responses of Arctic charr, Salvelinus alpinus, to environmental...