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At least 1,063 records · Page 59Linked to original sources
PubMed1981

Immunofluorescent and structural features of cells in the intervascular stroma of the amphibian carotid labyrinth.

The amphibian carotid labyrinth consists of a pars cavernosa, the main chamber of which is in communication with both the base of the external carotid artery, and the vessels of the labyrinthine pars capillaris. On the walls of the main chamber is a network of thick strands of connective tissue and modified smooth muscle cells surrounding the openings into the p. capillaris. These openings lead into wide-diameter atrial vessels, which in turn branch to form the short narrow-diameter vessels. The short vessels form the major component of the labyrinth. A few extremely narrow-diameter vessels are also present. The short vessels open into the roots of the internal carotid artery on the ventral aspect of the carotid labyrinth. The intervascular stroma of the p. capillaris contains numerous stellate and bipolar cells. These cells give a positive response to an immunofluorescent technique specific for smooth muscle myosin and tropomyosin. As the ultrastructural features of these cells are comparable in many respects to smooth muscle, they have been designated as modified smooth muscle cells. It is proposed that these cells act in both an active and passive fashion in maintaining the luminal dimensions of the short vessels relatively constant.

Animals↗
PubMed1995

Structural features and phylogeny of the actin gene of Chondrus crispus (Gigartinales, Rhodophyta).

We have characterized the cDNA and genomic sequences that encode actin from the multicellular red alga Chondrus crispus. Southern-blot analysis indicates that the C. crispus actin gene (ChAc) is present as a single copy. Northern analysis shows that, like the GapA gene, the actin gene is well expressed in gametophytes but weakly in protoplasts. Compared to actin genes of animals, fungi, green plants and oomycetes, that of C. crispus displays a higher evolutionary rate and does not show any of the amino-acid signatures characteristic of the other lineages. As previously described for GapA, ChAc is interrupted by a single intron at the beginning of the coding region. The site of initiation of transcription was characterized by RNAse protection. The promoter region displays a CAAT box but lacks a canonical TATA motif. Other noticeable features, such as a high content of pyrimidines as well as a 14-nt motif found in both the 5'-untranslated region and the intron, were observed.

Actins↗
PubMed1981

Structural features and selective expression of three Ly-5+ cell-surface molecules.

Conventional Ly-5 alloantisera precipitate cell-surface molecules of three sizes: 200K, 205K, and 220K. In SDS-PAGE, the rat monoclonal antibody 74/8' precipitates the same three molecules from both Ly-5.1 and Ly-5.2 cells. Cleveland mapping of the three molecules, precipitated by reaction of conventional Ly-5 alloantisera or 74/8' monoclonal antibody with lysates of 125I-labeled cells, disclosed no differences among the three molecular forms, but markedly distinguished all three Ly-5.1 molecules from all three Ly-5.2 molecules. Each of the three molecular forms can be expressed independently of the other two by cloned culture lines of Ly-5+ cells of different hematopoietic lineage. All of the seven cloned lines tested expressed only one form. However, two of the seven uncloned culture lines tested, plasmacytoma MOPC-70A and the X.1 putative macrophage line which originated from an SJL tumor, yielded both 200K and 205K forms.

Animals↗
PubMed1982

Structural features of the rat small intestinal microvillus membrane in acute experimental diabetes.

Experimentally induced diabetes enhances the specific activity of several microvillus membrane proteins in the rat small intestine. The increase in the specific activity of sucrase-isomaltase has been shown by others to be due to an increase in enzyme protein, raising the possibility that diabetes induces a generalized increase in microvillus membrane proteins. Since intramembrane particles (IMPs) seen on freeze-fracture replicas of microvillus membranes are thought to represent integral membrane proteins, we compared microvillus IMP densities in diabetic rats with those in control rats. In addition, mucosal sucrase, maltase, and alkaline phosphatase specific activities were measured in all animals. Diabetic rats had significantly increased sucrase and maltase but not alkaline phosphatase specific activities compared with control rats. The density of microvillus IMPs on both the protoplasmic and extracellular fracture faces of undifferentiated crypt cells and villus absorptive cells was not increased in experimental diabetes. These data indicate that diabetes does not result in a generalized increase in microvillus membrane proteins. Thus the enhanced activity of microvillus membrane proteins in diabetes appears to be highly selective.

Acute Disease↗
PubMed1994

Structural features of mag, a gypsy-like retrotransposon of Bombyx mori, with unusual short terminal repeats.

Mag is a retrotransposon found as an insert in the Sericin 2 gene. It is present in a few copies--4 to 15--dispersed in the genome of different strains of Bombyx mori as well as in Bombyx mandarina. Flanked by a 5 bp target sequence with no sequence specificity, it is bordered by direct repeats of 77 nucleotides. Despite their unusual short size, these terminal repeats and their immediately adjacent sequences present all the signals necessary for transcription into genomic RNA and for reverse transcription. Mag contains two overlapping open reading frames which are organized as the gag and pol genes of retroviruses and encode putative nucleic acid binding peptide, protease, reverse transcriptase, RNase H and endonuclease in this order. Sequence comparison of these proteins places mag within the gypsy group of LTR retrotransposons next to the echinoderm element SURL.

Amino Acid Sequence↗
PubMed1993

Structural features of a multisubstate cardiac mitoplast anion channel: inferences from single channel recording.

Ion channels from sheep cardiac mitoplast (inverted inner mitochondrial membrane vesicle) preparations were incorporated into voltage-clamped planar lipid bilayers. A low-conductance anion channel (approximately 40 or approximately 85 pS in symmetric 300 or 550 mM choline Cl, respectively), characterized by the presence of two well-defined substates, at approximately 25 and approximately 50% of the fully open level, was studied in detail. The substate behavior was consistent with a multibarelled channel containing four functionally coupled pores. At negative (cis-trans) membrane potentials, the putative protomers appeared to gate with substantial positive cooperativity, accounting for the apparent absence of a approximately 75% sublevel. At positive holding potentials, allosteric promoter interactions were more complicated, and the channel complex could be modeled as a dimer of dimers. The protochannels in one dimer ("dimer A") appeared to open independently of each other, and with a relatively high probability, while the monomers comprising the second dimer ("dimer B") were functionally coupled, could only open if both protomers in dimer A were open, and closed as soon as one of the monomers in dimer A shut. The channels also displayed Ca(2+)-(and Mg(2+)-) sensitive rectification related to bilayer lipid surface charge. By assuming that Ca2+ acted solely by screening surface charge, the membrane surface potential profile was used as a "microscopic ruler" to place one month of the channel within 10-11 A of the bilayer surface.

Animals↗
PubMed2001

Microfocus small angle X-ray scattering reveals structural features in archaeological bone samples: detection of changes in bone mineral habit and size.

Microfocus X-ray scattering provides a powerful nondestructive technique capable of providing important information about the size, habit, and arrangement of mineral crystals in bone. The technique is capable of probing textural differences in a sample at a micron scale resolution. The study presented here involved the analysis of a number of archaeological bones by microfocus X-ray scattering at the ESRF Grenoble in order to determine local changes in mineral durability. The results showed that regions of bone with a modified microscopic morphology contained a greater dispersion of crystal shape when compared with more intact regions and control contemporary bone samples, but the crystal thickness values showed similar consistency. We speculate that the persistence of collagen in the archaeological bone may allow diagenetic remodeling of bone in terms of crystallite shape but defines the size of remodelled crystallites. The ability to detect such local changes in texture has wide potential for determining crystal characteristics in healthy and diseased bone samples.

Archaeology↗
PubMed2005

The mitochondrial genome of Xiphinema americanum sensu stricto (Nematoda: Enoplea): considerable economization in the length and structural features of encoded genes.

The complete sequence of the mitochondrial genome of the plant parasitic nematode Xiphinema americanum sensu stricto has been determined. At 12626bp it is the smallest metazoan mitochondrial genome reported to date. Genes are transcribed from both strands. Genes coding for 12 proteins, 2 rRNAs and 17 putative tRNAs (with the tRNA-C, I, N, S1, S2 missing) are predicted from the sequence. The arrangement of genes within the X. americanum mitochondrial genome is unique and includes gene overlaps. Comparisons with the mtDNA of other nematodes show that the small size of the X. americanum mtDNA is due to a combination of factors. The two mitochondrial rRNA genes are considerably smaller than those of other nematodes, with most of the protein encoding and tRNA genes also slightly smaller. In addition, five tRNAs genes are absent, lengthy noncoding regions are not present in the mtDNA, and several gene overlaps are present.

Animals↗
PubMed2006

Molecular organization of 5S rDNAs in Rajidae (Chondrichthyes): Structural features and evolution of piscine 5S rRNA genes and nontranscribed intergenic spacers.

The genomic and gene organisation of 5S rDNA clusters have been extensively characterized in bony fish and eukaryotes, providing general issues for understanding the molecular evolution of this multigene DNA family. By contrast, the 5S rDNA features have been rarely investigated in cartilaginous fish (only three species). Here, we provide evidence for a dual 5S rDNA gene system in the Rajidae by sequence analysis of the coding region (5S) and adjacent nontranscribed spacer (NTS) in five Mediterranean species of rays (Rajidae), and in a large number of piscine taxa including lampreys and bony fish. As documented in several bony fish, two functional 5S rDNA types were found here also in the rajid genome: a short one (I) and a long one (II), distinguished by distinct 5S and NTS sequences. That the ancestral piscine genome had these two 5S rDNA loci might be argued from the occurrence of homologous dual gene systems that exist in several fish taxa and from 5S phylogenetic relationships. An extensive analysis of NTS-II sequences of Rajidae and Dasyatidae revealed the occurrence of large simple sequence repeat (SSR) regions that are formed by microsatellite arrays. The localization and organization of SSR within the NTS-II are conserved in Rajiformes since the Upper Cretaceous. The direct correlation between the SSRs extension and the NTS length indicated that they might play a role in the maintenance of the larger 5S rDNA clusters in rays. The phylogenetic analysis indicated that NTS-II is a valuable systematic tool limited to distantly related taxa of Rajiformes.

Animals↗
PubMed2001

Structural features of the mdg1 lineage of the Ty3/gypsy group of LTR retrotransposons inferred from the phylogenetic analyses of its open reading frames.

The increasing amount of data generated in recent years has opened the way to exhaustive studies of the relationships among different members of the Ty3/gypsy group of LTR retrotransposons, a widespread group of eukaryotic transposable elements. Former research led to the identification of several independent lineages within this group. One of the worse represented of them is that of mdg1, integrated so far only by the Drosophila retrotransposons mdg1 and 412. Our exhaustive database searches indicate the existence of three other Drosophila members of this lineage. Two of them correspond to elements already known, namely, Stalker and blood, but the third one is a new element, which we have called Pilgrim. This element is well represented within the D. melanogaster genome, as revealed by our Southern blot analysis of different strains. The case of Stalker is particularly remarkable, since its phylogenetic relationships clearly point to the mosaic origin of its genome. Finally, our analysis of the evolution of a small ORF preserved within the 5' leader region of these elements indicates different evolutionary rates, presumably as a result of distinct selective constraints.

Amino Acid Sequence↗
PubMed2002

Structural features of the lac promoter affecting gusA expression in Lactobacillus casei.

With the aim of designing efficient expression systems for Lactobacillus casei, different factors affecting gene expression from the strong and highly modulated lac promoter have been systematically analyzed, by using the Escherichia coli beta-glucuronidase gene (gusA) as reporter. The activity of this enzyme (GUS) was quantified when plac:: gusA fusions were cloned in plasmids with different copy number or when gusA was inserted in the chromosomal lactose operon (single copy). Results showed a clear gene dosage effect and a positive influence of the native lac operon transcription and translation signals on GUS expression.

Amino Acid Sequence↗