Detoxification of ochratoxin A,a food contaminant: Prevention of growth of Aspergillus ochraceus and its production of ochratoxin A

The toxicity of ochratoxin A (OTA), a mycotoxin produced by fungi ofAspergillus orPenicillium genera is now well documented. Its nephrotoxicity, immunosuppression, teratogenicity, and carcinogenicity have been widely studied. Physical and biochemical methods have been studied to prevent these toxinogenicAspergillus andPenicillium from producing OTA, and/or to destroy the mycotoxin when already produced in a liquid or a solid medium. Repeated freezing at ? 20?C and thawing at + 26?C aleatory reduce OTA production in a liquid medium. Exposure to UV B for different periods of time is efficient in preventing OTA production in a liquid medium. Gamma-irradiation from 2 to 5 kGy gives good results in preventing the production of OTA or destroying it when already produced. Carboxypeptidase is very efficient at 5 units/50 ml in a liquid medium for cleaving the OTA already produced.     

Cloning and analysis of structural genes from Streptomyces pristinaespiralis encoding enzymes involved in the conversion of pristinamycin IIB to pristinamycin IIA (PIIA): PIIA synthase and NADH:riboflavin 5'-phosphate oxidoreductase.

In Streptomyces pristinaespiralis, two enzymes are necessary for conversion of pristinamycin IIB (PIIB) to pristinamycin IIA (PIIA), the major component of pristinamycin (D. Thibaut, N. Ratet, D. Bisch, D. Faucher, L. Debussche, and F. Blanche, J. Bacteriol. 177:5199-5205, 1995); these enzymes are PIIA synthase, a heterodimer composed of the SnaA and SnaB proteins, which catalyzes the oxidation of PIIB to PIIA, and the NADH:riboflavin 5'-phosphate oxidoreductase (hereafter called FMN reductase), the SnaC protein, which provides the reduced form of flavin mononucleotide for the reaction. By using oligonucleotide probes designed from limited peptide sequence information of the purified proteins, the corresponding genes were cloned from a genomic library of S. pristinaespiralis. SnaA and SnaB showed no significant similarity with proteins from databases, but SnaA and SnaB had similar protein domains. Disruption of the snaA gene in S. pristinaespiralis led to accumulation of PIIB. Complementation of a S. pristinaespiralis PIIA-PIIB+ mutant with the snaA and snaB genes, cloned in a low-copy-number plasmid, partially restored production of PIIA. The deduced amino acid sequence of the snaC gene showed no similarity to the sequences of other FMN reductases but was 39% identical with the product of the actVB gene of the actinorhodin cluster of Streptomyces coelicolor A(3)2, likely to be involved in the dimerization step of actinorhodin biosynthesis. Furthermore, an S. coelicolor A(3)2 mutant blocked in this step was successfully complemented by the snaC gene, restoring the production of actinorhodin.     

Structural and biological roles of glycosylations in pulmonary angiotensin I-converting enzyme

We enzymatically deglycosylated pig lung angiotensin I-convertingenzyme (ACE) to study the involvement of its glycanic chainsin its physicochemical and catalytic properties. The effectsof endoglycosidases F₂ and H, and of N-glycanase were assessedby ACE mobility in SDS-PAGE. N-Glycanase only was completelyeffective with or without previous denaturation, leading toa shift in ACE M_r from 172 to 135 kDa; endoglycosidase F₂ producedthe same shift but only without previous denaturation. DeglycosylatedACE had the same kcat as native ACE for the substrate hippuryl-histidyl-leucine,and an identical Stokes radius as measured by size-exclusionhigh performance liquid chromatography. Neuraminidase had noeffect on ACE Stokes radius but slightly decreased its kcatwhich could be related to variations in ionization of the activesite. The isoelectric point of ACE, as, determined by isoelectricfocusing, increased from 4.5–4.8 to 5.0–5.3 aftereither endoglycosidase F₂ or neuraminidase digestion, but stillwith microheterogeneities which thus did not seem to be relatedto ACE glycans. Deglycosylated ACE did not bind onto agaroselectinsin contrast to native ACE which bound strongly to concanavalinA showing interactions involving oligomannosidic or biantennaryand sialylated N-acetyl-lactosaminic isoglycans. Finally, tunicamycin,an inhibitor of N-glycosylation, did not modify ACE secretionby endothelial cells. Thus, ACE glycans have no drastic effectson structural and biological properties of the protein, butthey may have a functional role on intracellular targeting ofboth secreted and membrane-bound ACE isoforms, also for theprotection of the soluble plasma form against hepatic lectinsand the maintenance of its hydrosolubility. converting enzyme (peptidyldipeptidase EC.3.4.15.1) endothelium glycosidases lectins     

Phenotypically Vif- human immunodeficiency virus type 1 is produced by chronically infected restrictive cells.

The permissivity of CD4+ transformed T cells for the replication of human immunodeficiency virus type 1 (HIV-1) vif mutants varies widely between different cell lines. Mutant vif-negative viruses propagate normally in permissive CD4+ cell lines but are unable to establish a productive infection in restrictive cell lines such as H9. As a consequence, elucidation of the function of Vif has been considerably hampered by the inherent difficulty in obtaining a stable source of authentically replication-defective vif-negative viral particles produced by restrictive cells. vif-negative, vpr-negative HIV-1 strain NDK stock, produced by the permissive SupT1 cell line, was used to infect restrictive H9 cells. By using a high multiplicity, infection of H9 cells was achieved, leading to persistent production of viral particles displaying a dramatically reduced infectious virus titer when measured in a single-cycle infectivity assay. Although these viral particles were unable to further propagate in H9 cells, they could replicate normally in CEM and SupT1 cells. Comparison of unprocessed and processed Gag proteins in the persistently produced vif-negative viral particles revealed no defect in the processing of polypeptide precursors, with no inversion of the Pr55gag/p24 ratio. In addition, there was no defect in Env incorporation for the vif-negative viral particles. Despite their apparently normal protein content, these particles were morphologically abnormal when examined by transmission electron microscopy, displaying a previously described abnormally condensed nucleoid. Chronically infected restrictive cell lines producing stable levels of phenotypically vif-negative HIV-1 particles could prove particularly useful in further studies on the function of Vif in the virus life cycle.     

Two modules from the hypersuppressive rho mitochondrial DNA are required for plasmid replication in yeast

In the yeast hypersuppressive (HS) rho⁻ mutants most of the mitochondrial genome is deleted, but the remainder containing one of the three rep sequences is amplified. One of these sequences, rep2, and its flanking regions have been previously cloned and reported to promote autonomous plasmid replication in yeast. The present study suggests that the Ars activity associated with this HS rho⁻ mitochondrial DNA (mtDNA) fragment is due to the presence in cis of at least two modules: (i) the 11-bp consensus sequence 5′-^A_TAAA^C_TATAAA^A_T-3′, common to several ars sequences, and (ii) a palindromic sequence of the mitochondrial replicator. Proper spacing between the two modules, which varies from about 100 to 200 bp, is required for the Ars ⁺ activity.     

Detailed cell cycle analysis in human lymphocytes; Application to γ-irradiated cells

Summary A method based on BrdU incorporation for analyzing in detail the kinetics of the cell cycle is described. The S phase has been subdivided into five subphases, each recognizable by their BrdU incorporation pattern at metaphase. The method can be useful for the study of abnormal cell cycles, and may have particular application in mutagenesis studies concerning the various subphases of the S phase, without using synchronization techniques. An application of the method is described, showing that -irradiation, during the course of the S phase, leads to a lack of cells which were in early S phase at the time of irradiation. This finding can be related either to a higher lethality at this stage of the cell cycle or to a delay in completion of DNA replication after irradiation.Hoider of a C.E.C. scholarship     

Secondary trisomy 1 q due to a reciprocal maternal translocation]

The authors report a case of partial trisomy 1 q due to a maternal balanced translocation : t(1 ; 4) (q 32 : p 16). The evocative malformations of trisomy 1 q and monosomy 4 p are discussed and compared to seven others from the literature. Then the interest of the chromosomical prenatal diagnosis and the significance of familial genetic studies are showed.     

Sequences homologous to Tc(s) transposable elements ofCaenorhabditis elegans are widely distributed in the phylum nematoda

Summary To have a better understanding of the evolutionary history of mobile elements within the nematodes, we examined the distribution and the conservation of homologues to transposable elements fromCaenorhabditis elegans (Tc1, Tc2, Tc3, Tc4, Tc5, and FB1) in 19 nematode species belonging to the class Secernentea. Our results show that Tc1 elements display a distribution restricted to the family Rhabditidae with poor conservation. The Tc2 and FB1 homologous elements have the same patchy distribution within the Rhabditidae. They were only found inCaenorhabditis and inTeratorhabditis. The Tc3 element is widely distributed among nematode species. Tc3 homologous elements are present in the majority of the Rhabditidae but also in two genera within the family Panagrolaimidae, and inBursaphelenchus, which belongs to the order Aphelenchida. Tc4 and Tc5 homologues show the most limited distribution of all tested elements, being strictly limited toC. elegans. These data indicate that in some cases, the distribution of transposable elements in the nematode cannot be explained by strict vertical transmission. The distribution of Tc3, Tc4, and Tc5 suggests that horizontal transmission may have occurred between reproductively isolated species during their evolutionary history.