Molecular cloning and complete nucleotide sequence of the repeated unit and flanking gene of the scallop Pecten maximus mitochondrial DNA: Putative replication origin features

In the bivalve mollusc Pecten maximus, the size of the mitochondrial DNA molecules ranges from 20 to 25.8 kbp. This variability is mainly correlated with the occurrence of a variable domain composed with two to five 1.6-kbp repeated units tandemly arrayed in the genome. DNA fragments spanning the 1,586-base-pair-long repeated element and the nearest flanking gene have been cloned and sequenced. This sequence was analyzed regarding its base composition and potential secondary structures. The repeated unit domain was positioned and oriented with regard to the known flanking gene. It ends 2 base pairs upstream relative to the beginning of the tRNA^gly gene. The peculiar properties of the repeated unit were compared with those of the 1,442-bp repeated element found in the mitochondrial genome of the deep sea scallop Placopecten magellanicus. This comparison provided evidence for the absence of nucleotide conservation, except for a small sequence engaged in a secondary structure, but argued for a strong pressure maintaining domains with specific nucleotide content. A possible role for the conserved sequence is discussed.Correspondence to: A. Rigaa     

Identification of members of gene families in Arabidopsis thaliana by contig construction from partial cDNA sequences: 106 genes encoding 50 cytoplasmic ribosomal proteins

Partial cDNA sequencing to obtain expressed sequence tags (ESTs) has led to the identification of tags to about 8000 of the estimated 20 000 genes in Arabidopsis thaliana . This figure represents four to five times the number of complete coding sequences from this organism available in international databases. In contrast to mammals, many proteins are encoded by multigene families in A. thaliana . Using ribosomal protein gene families as an example, it is possible to construct relatively long sequences from overlapping ESTs which are of sufficiently high quality to be able to unambiguously identify tags to individual members of multigene families, even when the sequences are highly conserved. A total of 106 genes encoding 50 different cytoplasmic ribosomal protein types have been identified, most proteins being encoded by at least two and up to four genes. Coding sequences of members of individual gene families are almost always very highly conserved and derived amino acid sequences are almost, if not completely, identical in the vast majority of cases. Sequence divergence is observed in untranslated regions which allows the definition of gene-specific probes. The method can be used to construct high-quality tags to any protein.     

Hypoxia Dramatically Increases the Nonspecific Transport of Blood-Borne Proteins to the Brain

Abstract: Increased cerebrovascular permeability is an important factor for the development of cerebral edema. To investigate the effect of hypoxia on the transport of blood-borne proteins to the brain, we used a cell culture model of the blood-brain barrier (BBB) consisting of a coculture of brain capillary endothelial cells and astrocytes that closely mimics the in vivo situation. The permeability of albumin, a marker of the nonspecific transcellular route, is extremely low in this in vitro model of the BBB. After hypoxia, a huge increase in the permeability of albumin is detected. Despite the opening of the tight junctions already demonstrated after hypoxia, the increase in the permeability of albumin is mainly attributed to an increase of the nonspecific vesicular transport in the cell, attested by the temperature dependence of the phenomenon and the visualization of labeled apotransferrin in the cytoplasm. The increase of this pathway could participate in the development of brain edema during hypoxia.     

Glutamine synthetase (GS) expression is reduced in senile dementia of the Alzheimer type

Glutamine synthetase (GS), a metabolic marker of the mature astrocyte, was investigated in the temporal neocortex of postmortem brain samples of 8 cases, either not demented or affected by senile dementia of the Alzheimer type. A negative correlation between the GS protein level and the density of both classical A4 deposits and senile plaques was evidenced. Such a correlation for GS underlies a dysfunction of the astroglial metabolism and particularly of the glutamate and ammonia neutralization. Since GS is sensitive to oxidative lesioning, the changes in GS level that were observed, occurring at the posttranslational stage, might reflect oxidative damage and have severe consequences on the pathological cascade of events.     

Some significant differences in wall chemistry among four commercial Agaricus bisporus strains

Significant differences in gross wall chemical composition were detected in four commercial Agaricus bisporus strains. All were grown under the same conditions and their walls prepared by a mild method of breakage. A more detailed analysis of the wall fractions, isolated by means of their distinct solubilities, also showed striking structural differences among the four strains studied. The detected differences, not only in the overall composition of the wall but also in the polysaccharide structure, could assist in the characterization of strains and/or varieties of the commercial basidiomycete A. bisporus.     

In vitro autoradiographic localization of vasoactive intestinal peptide (VIP) binding sites in the rat central nervous system

This paper describes the autoradiographic distribution of VIP binding sites in the rat central nervous system using monoiodinated ¹²³I-labeled VIP. High densities of VIP binding sites are observed in the granular layer of the dorsal dentate gyrus of the hippocampus, the basolateral amygdaloid nucleus, the dorsolateral and median geniculate nuclei of the thalamus as well as in the ventral part of the hypothalamic dorsomedial nucleus.     

Polyploidy and aspartate-transcarbamylase activity in Hippocrepis comosa L.

The DNA content of plants which were sampled in natural di-, tetra- and hexaploid populations of Hippocrepis comosa L. was estimated and the aspartate transcarbamylase activities of the corresponding cell-free extracts were compared. The amount of DNA is not exactly proportional to the number of genomes. The three kinds of populations do not differ in their aspartate transcarbamylase specific activity. While the enzyme properties are identical in the extracts derived from the diploid and hexaploid plants, the aspartate transcarbamylase present in the tetraploid cytotype shows a slightly lower affinity for one of its substrates and a significantly lower sensitivity to the feedback inhibitor UTP which is still observed after partial purification. These properties might be related to the previously reported greater ability of the tetraploid cytotype to adapt to a variety of biotopes.Abbreviations ATCase aspartate transcarbamylase - CAP carbamylphosphate - EDTA ethylenediaminetetracetic acid - Tris trihydroxymethylaminomethane - AMP adenosine monophosphate - ATP adenosine triphosphate - CMP cytidine monophosphate - CTP cytidine triphosphate - UMP uridine monophosphate - UTP uridine triphosphate     

Spot position of rat liver ribosomal proteins by four different two-dimensional electrophoreses in polyacrylamide gel

Summary Separation of the proteins from rat liver 40S and 60S ribosomal subunits and polysomes was done in four different two-dimensional polyacrylamide gel electrophoresis systems. The first dimension was run at acidic or basic pH, the second dimension either with sodium dodecyl sulphate or at acidic pH in 18% acrylamide. The position of each individual protein of both subunits and polysomes was determined in each system. This identification resulted from a new method avoiding any previous purification of individual proteins. The new proposed uniform nomenclature for mammalian ribosomal proteins (McConkey et al. in press) was used for numbering the proteins in the four systems.     

Biochemical evidence for the non-inactivation of the steroid sulfatase locus in human placenta and fibroblasts

Summary Steroid sulfatase activities are significantly higher in placentas obtained after the birth of girls than after the birth of boys, and also in female fibroblasts compared to male strains. This constitutes biochemical evidence for the non-inactivation of the X-linked sulfatase locus. No hydrolytic activity is found in the fibroblasts of ichthyotic boys. Heterozygosity is demonstrated in the fibroblasts of the four mothers studied, as they have steroid sulfatase activity of less or equivalent to the normal male value.