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L R Evans

Publications and source records attributed to L R Evans.

At least 19 recordsLinked to original sources
PubMed2001

The structure of a polysaccharide from infectious strains of Burkholderia cepacia.

The structure of an acidic exopolysaccharide (EPS) from eight strains of Burkholderia cepacia has been investigated by methylation and sugar analysis, periodate oxidation-Smith degradation, and partial acid-hydrolysis. An enzyme preparation obtained from the same organisms producing the EPS was also used to depolymerize the polysaccharide. Detailed NMR studies of the chemical and enzymatic degradation products showed that this EPS consists of a highly branched heptasaccharide-repeating unit with the following structure: [abstract: see text]. About three O-acetyl groups per repeating unit are present at undetermined positions.

Animals↗
PubMed2000

Structure of succinoglycan from an infectious strain of Agrobacterium radiobacter.

The exopolysaccharide produced by a cystic fibrosis clinical isolate of Agrobacterium radiobacter was shown by monosaccharide and methylation analyses, degradation with succinoglycanase and NMR analysis to be a succinoglycan with the structure shown below. (S)-pyruvic acid is found stoichiometrically as 4,6-O-ketal substituent of terminal glucose. Succinic acid is present in 40% of the repeating units and it is attached to O-6 of the 3-linked glucose next to the pyruvate carrying sugar. Some evidence is found that a small amount of succinic acid (ca. 6% of the total) is linked to O-6 of another undetermined glucose. [structure: see text]

Carbohydrate Sequence↗
PubMed1998

Disruption of the Saccharomyces cerevisiae YAP3 gene reduces the proteolytic degradation of secreted recombinant human albumin.

Expression of recombinant human albumin (rHA) in Saccharomyces cerevisiae resulted in secretion of both mature albumin and a 45 kDa degradation product, comprising an N-terminal fragment of rHA with heterogeneous C-termini between residues 403 and 409 (Geisow et al., 1991). Site-directed mutagenesis of the human albumin gene (HA) to change Arg410 to Ala (R410A) caused a significant reduction in the amount of fragment produced. Mutation of the adjacent dibasic site Lys413 Lys414 had little effect in isolation, but in combination with the R410A mutation resulted in a further reduction in the amount of rHA fragment produced. This reduction could be duplicated with nature-identical rHA by disruption of the gene for an aspartyl protease (YAP3), alone or in conjunction with disruption of the KEX2 gene. Disruption of KEX2 alone did not result in any improvement in the degree of degradation of the rHA. Reduced degradation was also observed when an rHA-human growth hormone fusion protein was secreted from a yap3 strain, suggesting that such strains may have a general utility for heterologous protein secretion.

Albumins↗
PubMed1997

Testicular expression of inhibin and activin subunits and follistatin in the rat and human fetus and neonate and during postnatal development in the rat.

Inhibins, activins, and follistatins are all believed to play roles in the regulation of FSH secretion by the pituitary and in the paracrine regulation of testis function. Previous studies have resulted in conflicting data on the pattern of expression of the inhibin/activin subunits, and little information on expression of follistatin during fetal/neonatal life. We have made use of new, highly specific monoclonal antibodies and fixed tissue sections from fetal, neonatal, and adult rats, and limited amounts of fetal and neonatal human testis, to undertake a detailed immunocytochemical study of the pattern of expression of these regulatory proteins. In the rat, positive immunostaining for the alpha-subunit of inhibin (alpha) was first detectable on day 14.5 post coitum (p.c.), the first day on which the testis could be morphologically distinguished from the ovary. During fetal life, the alpha-immunostaining was most prominent in the fetal Leydig cells. In Sertoli cells, alpha-immunostaining was slightly stronger on days 14.5 and 15.5 p.c. compared with 16.5-20.5. After birth, alpha-immunostaining remained intense in fetal Leydig cells but declined following their replacement with their adult-type counterparts; in contrast, alpha-subunit increased in Sertoli cells immediately after birth. Immunostaining with antibodies specific to betaB-subunit showed a similar pattern to that of the alpha-subunit, except that positive immunostaining was first detectable on day 16.5 p.c., 2 days later than immunostaining for the alpha-subunit. The pattern of betaB-immunostaining in postnatal samples paralleled that of the alpha-subunit. Immunostaining using antibodies against the betaA-subunit did not produce any significant reaction product in any sample. Follistatin was undetectable in the fetal rat testis but appeared in the Leydig cells immediately after birth and its expression remained intense throughout postnatal development and in adult testis. No evidence was obtained for expression of either the inhibin/activin subunits or follistatin in the germ cells, peritubular myoid cells, or other interstitial cells in any of the sections examined. In the human fetal testis, both alpha- and betaB-subunits were immunodetectable at 16, 18, and 24 weeks gestation in Sertoli and Leydig cells, with stronger immunostaining in Sertoli cells at 24 weeks. Postnatally at 4 months, immunoexpression of the betaB-subunit was no longer detectable, whereas the alpha-immunostaining became weaker but was still present in both Sertoli and Leydig cells. No positive immunostaining for betaA-subunit or follistatin was detectable at any time point studied. In conclusion, we have shown that, in the rat testis, the majority of inhibin alpha-subunit and inhibin/activin betaB-subunit is immunolocalized to the fetal-type Leydig cells during fetal/neonatal life but, following birth, immunoexpression in the Sertoli cells of both subunits increases markedly while follistatin is immunodetectable only postnatally.

Activins↗
PubMed1991

A complex family of class-II restriction endonucleases, DsaI-VI, in Dactylococcopsis salina.

A series of class-II restriction endonucleases (ENases) was discovered in the halophilic, phototrophic, gas-vacuolated cyanobacterium Dactylococcopsis salina sp. nov. The six novel enzymes are characterized by the following recognition sequences and cut positions: 5'-C decreases CRYGG-3' (DsaI); 5'-GG decreases CC-3' (DsaII); 5'-R decreases GATCY-3' (DsaIII); 5'-G decreases GWCC-3' (DsaIV); 5'-decreases CCNGG-3' (DsaV); and 5'-GTMKAC-3' (DsaVI), where W = A or T, M = A or C, K = G or T, and N = A, G, C or T. In addition, traces of further possible activity were detected. DsaI has a novel sequence specificity and DsaV is an isoschizomer of ScrFI, but with a novel cut specificity. A purification procedure was established to separate all six ENases, resulting in their isolation free of contaminating nuclease activities. DsaI cleavage is influenced by N6-methyladenine residues [derived from the Escherichia coli-encoded DNA methyltransferase (MTase) M.Eco damI] within the overlapping sequence, 5'-CCRYMGGATC-3'; DsaV hydrolysis is inhibited by a C-5-methylcytosine residue in its recognition sequence (5'-CMCNGG-3'), generated in some DsaV sites by the E. coli-encoded MTase, M.Eco dcmI.

Base Sequence↗
PubMed1991

Saccharomyces cerevisiae strains that overexpress heterologous proteins.

We describe a system that facilitates the selection of host mutants that overproduce a range of secreted and internally produced heterologous proteins in Saccharomyces cerevisiae. These mutants were initially selected for their ability to oversecrete recombinant human albumin (rHA), as detected by a direct visual assay that relies upon antibody precipitation in solid media. Yeast strains that were able to synthesize and secrete increased levels of rHA also produced elevated levels of internally expressed proteins including alpha 1-antitrypsin Pittsburgh variant and plasminogen activator inhibitor type 2.

Animals↗
PubMed1987

Construction of hybrid Tn501/Tn21 transposases in vivo: identification of a region of transposase conferring specificity of recognition of the 38-bp terminal inverted repeats.

In order to study the transposase enzymes of Class II prokaryotic transposable elements, we have constructed genes encoding hybrid transposase proteins. This was done by recombination in vivo between the tnpA genes of transposons Tn501 and Tn21. These hybrid genes can complement in trans a transposition-defective mutant of Tn501. The structures of the products of this complementation indicate whether the specificity of the hybrid transposase in recognising the 38 bp terminal inverted repeats is that of Tn501 or that of Tn21. The determinant of this specificity is in the N-terminal region of the transposase protein, between amino acids 28 and 216. The predicted amino acid sequences so far determined of transposases from the Class II family reveal an area of homology in this region.

Amino Acid Sequence↗
PubMed1984

Isolation and characterization of an alginase from mucoid strains of Pseudomonas aeruginosa.

Strains of Pseudomonas aeruginosa which produce an alginate-like slime polysaccharide were shown to also synthesize an intracellular enzyme which can degrade these polysaccharides and the seaweed alginic acids. The enzyme acts as an eliminase introducing delta 4,5 unsaturation into the uronic acid moiety. It appears to be a polymannuronide lyase which degrades the polysaccharides, depending on their uronic acid composition, to a series of oligosaccharides, the smallest of which is a disaccharide. L-Guluronic acid linkages are not split. The Pseudomonas alginase resembles other bacterial alginases and enzymes from molluscs but differs in some important properties, such as extent of degradation and linkage preference. Nonmucoid forms of the organism produce detectable but much lower amounts of enzyme.

Glycoside Hydrolases↗
PubMed1973

Production and characterization of the slime polysaccharide of Pseudomonas aeruginosa.

The slime polysaccharides produced by Pseudomonas aeruginosa isolated from a variety of human infections were investigated. Slime production in culture seemed optimal when adequate amounts of carbohydrate were present and under conditions of either high osmotic pressure or inadequate protein supply. The polysaccharides produced by the organisms were similar to each other, to the slime of Azotobacter vinelandii, and to seaweed alginic acids. They were composed of beta-1,4-linked d-mannuronic acid residues and variable amounts of its 5-epimer l-guluronic acid. All bacterial polymers contained o-acetyl groups which are absent in the alginates. The polysaccharides differed considerably in the ratio of mannuronic to guluronic acid content and in the number of o-acetyl groups. The particular composition of the slime was not found to be characteristic for the disease process from which the mucoid variants of P. aeruginosa were obtained.

Acetylation↗