YAC cloning of DNA embedded in an agarose matrix

Yeast artificial chromosome (YAC) cloning of DNA in agarose is an alternative method to cloning from aqueous solutions. It minimizes any shearing that may result from handling of high molecular weight DNA and can be done with nanogram to microgram amounts of material, which facilitates construction of YACs from sources of DNA other than genomic DNA isolated from cells. The average size of the YACs recovered (200-1000 kb) and efficiency of transformation of ligation products (200-1000 cfu/micrograms) are similar to those reported using aqueous protocols. This method has been used to construct chromosome specific YACs, and it should be possible to apply the technique to the construction of chromosome specific libraries using flow sorted chromosomes as source material, and the cloning of restriction fragments isolated by preparative pulsed field gel electrophoresis.     

Protamines in plant sperm

Sperm protamines have been isolated from representatives of three major plant groups: algae (Chara corallina ), bryophytes ( Marchantia polymorpha), and ferns ( Marsilea vestitia ). We previously reported the complete displacement of histones by protamines in Marchantia (Reynolds W F & Wolfe, S L, Exp cell res 116 (1978) 269 [8] ). Marchantia protamines appear as four components on acid-urea gels, whereas Chara and Marsilea protamines comigrate as a single band with a mobility comparable to salmon protamine. The amino acid compositions of the plant protamines show these to be arginine-rich, highly basic (35-42%) proteins which display overall similarity in amino acid composition (84-91%). The molecular weights of Chara and Marsilea protamines are approx. 4700-5300 D.     

Effects of chronic hyperinsulinaemia on hepatic enzymes involved in lipogenesis and carbohydrate metabolism in the young rat.

Chronic (6 days) hyperinsulinaemia in young rats produced lower blood glucose concentrations and augmented body- and liver-weight gain. The insulin-treated rats had increased hepatic activities of citrate-cleavage enzyme, 'malic' enzyme and high-substrate (6.6 mM-phosphoenolpyruvate) pyruvate kinase, and decreased glucose 6-phosphatase. There were no changes in activities of phosphoenolpyruvate carboxykinase, phosphofructokinase, low-substrate (1.3 mM-phosphoenolpyruvate) pyruvate kinase, glucokinase and hexokinase.     

An in situ assay for induced diphtheria-toxin-resistant mutants of diploid human fibroblasts

The sensitivity of diploid human fibroblasts to the cytotoxic effects of diphtheria toxin (DT) depended on the cell growth status. Exponentially growing cells treated with 10^?3-1 lethal flocculating units (LF) of DT/ml for 4 days survived with a frequency of 4 × 10^?4. However, the DT-resistant phenotype of colonies isolated under these conditions was not stable. When the growth of the cells had been arrested by confluence or deprivation of serum growth factors prior to treatment with DT (4 days, 10^?3-0.6 LF/ml), the survival decreased to 2 × 10^?6 and the resistance of isolated colonies was stable. An in situ assay for induced DT-resistant mutants was developed in order to avoid problems associated with the possible reduced viability of the mutants relative to that of wild-type cells. A reproducible and linear dose response was obtained for the induction of DT-resistant mutants by ethylnitrosourea. The mutants were induced with high frequency by this compound (e.g., 10^?3 mutants/viable cell at a 37% survival dose); complete expression of the mutant phenotype occurred after 6 generations of growth under nonselective conditions. Isolated mutant colonies showed stable resistance to DT and were cross-resistant to Pseudomonas aeruginosa exotoxin A.     

Estimating ecotoxicological risk and impact using indigenous aquatic microbial communities

Emphasis has increased on accuracy in predicting the effect that anthropogenic stress has on natural ecosystems. Although toxicity tests low in environmental realism, such as standardized single species procedures, have been useful in providing a certain degree of protection to human health and the environment, the accuracy of such tests for predicting the effects of anthropogenic activities on complex ecosystems is questionable. The use of indigenous communities of microorganisms to assess the hazard of toxicants in aquatic ecosystems has many advantages. Theoretical and practical aspects of microbial community tests are discussed, particularly in related to widely cited problems in the use of multispecies test systems for predicting hazard. Further standardization of testing protocols using microbial colonization dynamics is advocated on the basis of previous studies, which have shown these parameters to be useful in assessing risk and impact of hazardous substances in aquatic ecosystems.     

Preparation and properties of immobilized flavokinase.

Flavokinase (ATP: riboflavin 5'-phosphotransferase, EC 2.7.1.26) purified from rat liver by affinity chromatography, has been immobilized by amide linkage to omega-aminoalkyl-agarose beads. The immobilized enzyme differs from the soluble enzyme in having greater stability, slightly higher Km for the substrates, riboflavin and ATP, a broader pH optimum, and a lower energy of activation. These results suggest that the immobilized enzyme is influenced by the microenvironment of the bead and is subject to some degree of internal diffusional limitation. A small (3 ml), continuous, plug-flow reactor prepared with immobilized flavokinase effects 50% conversion of riboflavin to riboflavin 5'-phosphate (FMN) with a flow rate of 0.16 ml/min, which corresponds to an output of 5 nmol FMN/min. Immobilized flavokinase is effective for phosphorylating riboflavin and numerous riboflavin analogs and provides a facile method for preparing exclusively, unlike other synthetic methods, the 5'-phosphates.     

Synthetic flavinyl peptides related to the active site of mitochondrial monoamine oxidase. I. Chemical and spectral properties.

Various 8 alpha-sulfur-linked peptides related to the flavinyl peptides isolated from mitochondrial monoamine oxidase were synthesized in high yield and purity. The peptides, protected by an acetyl-blocking group on the amino terminus, were synthesized by conventional liquid-phase techniques and coupled to a tetraacetylriboflavin derivative activated in the 8alpha position. In some cases, the ribityl side chains of the flavinyl peptides were selectively deacetylated. In other cases, the thioether functions were oxidized to form sulfones. These flavinyl peptides were studied by uv-visible absorption and circular dichroic spectroscopies. A close correspondence in spectroscopic and other chemical properties indicated the identity of the synthetic and naturally obtained flavinyl peptides. Differences between the tetraacetylriboflavinyl and riboflavinyl peptides indicate an interaction between the ribityl side chain and thioether function in aqueous media. Evidence was obtained for an intramolecular complex between the tyrosyl and isoalloxazine moieties in aqueous media. Substitution in the 8alpha position was accompanied by an impairment of the protonation of the N1 position of the isoalloxazine ring and a lowering of the redox potential relative to the parent 8-methyflavins.     

GEF-H1 Mediated Control of NOD1 Dependent NF-κB Activation by Shigella Effectors

Shigella flexneri has evolved the ability to modify host cell function with intracellular active effectors to overcome the intestinal barrier. The detection of these microbial effectors and the initiation of innate immune responses are critical for rapid mucosal defense activation. The guanine nucleotide exchange factor H1 (GEF-H1) mediates RhoA activation required for cell invasion by the enteroinvasive pathogen Shigella flexneri. Surprisingly, GEF-H1 is requisite for NF-κB activation in response to Shigella infection. GEF-H1 interacts with NOD1 and is required for RIP2 dependent NF-κB activation by H-Ala-D-γGlu-DAP (γTriDAP). GEF-H1 is essential for NF-κB activation by the Shigella effectors IpgB2 and OspB, which were found to signal in a NOD1 and RhoA Kinase (ROCK) dependent manner. Our results demonstrate that GEF-H1 is a critical component of cellular defenses forming an intracellular sensing system with NOD1 for the detection of microbial effectors during cell invasion by pathogens.