Phenotypes and gene expression profiles of Saccharopolyspora erythraea rifampicin-resistant (rif) mutants affected in erythromycin production

Background  

There is evidence from previous works that bacterial secondary metabolism may be stimulated by genetic manipulation of RNA polymerase (RNAP). In this study we have used rifampicin selection as a strategy to genetically improve the erythromycin producer Saccharopolyspora erythraea.     

Glycerol-3-phosphate acyltransferases: Rate limiting enzymes of triacylglycerol biosynthesis

Four homologous isoforms of glycerol-3-phosphate acyltransferase (GPAT), each the product of a separate gene, catalyze the synthesis of lysophosphatidic acid from glycerol-3-phosphate and long-chain acyl-CoA. This step initiates the synthesis of all the glycerolipids and evidence from gain-of-function and loss-of-function studies in mice and in cell culture strongly suggests that each isoform contributes to the synthesis of triacylglycerol. Much work remains to fully delineate the regulation of each GPAT isoform and its individual role in triacylglycerol synthesis.     

Sexual and asexual development: two distinct programs producing the same tunicate

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The effect of acridine orange on the structure of ribosomes

Exposure of Escherichia coli MRE-600 ribosomes to acridine orange (AO) at low ionic strength (1mM Tris-acetate pH 7.4) results in quantitative binding of the dye. Under our experimental conditions about a few hundred dye molecules can be bound to any one of the 30, 50, or 70-S particles. AO causes the 30 and the 50-S subunits to form ribosomal aggregates of approximate sedimentation constants of 70 and 100-S.     

Changes in avoidance behaviour following ethanol treatment in rats of different ages

Avoidance learning and pain sensitivity were studied in rats after chronic ethanol administration (1.1 to 1.7 g per kg b.w. in drinking water) at prenatal, adolescent and adult ages. The behavioural reactions were tested in adulthood by studying passive and active avoidance learning and the threshold of pain sensitivity to electric tail shock. Chronic ethanol consumption led to an impairment of avoidance learning and to hyperalgesia in each experimental series, although the alterations were greater in the prenatally treated groups. The experimental observations are discussed in the light of fetal alcohol syndrome.     

Abnormal stomatal behavior and root resistance,and hormonal imbalance in three wilty mutants of tomato

Three wilty mutants of tomato, flacca, sitiens, and notabilis, were compared with two control normal cultivars, Rheinlands Ruhm and Lukullus, for concentration of abscisic acid and root resistance to water flow. In addition, the three mutants treated with abscisic acid during development were compared with control mutant plants for stomatal opening and root resistance. The hormonal concentration was estimated by coleoptile assay and gas chromatography. Stomatal opening was estimated by measuring rate of transpiration and by examining leaf imprints. Root resistance was estimated by measuring the amount of exudate from roots of decapitated plants and the difference between the osmotic pressure of the exudate and the root medium. A lower level of abscisic acid was found in all three mutants as compared with the control normal plants. In addition, root resistance to water flow was higher in the three mutants than in the control normal types. All three mutants completely reverted to normal phenotypically, including stomatal and root resistances, when treated with abscisic acid. It has been suggested that the first hormonal change in the mutants is that of abscisic acid, and from it proceed the other changes.This work was supported in part by a research grant from the Ford Foundation (Ford-6, A-VII).     

Alveolar dehiscences and fenestrae in dried south African Negro mandibles

The buccal and lingual roots of 1077 teeth from 100 mandibles of South African Negroes were examined for the presence of dehiscences and fenestrae. All specimens were obtained from cadavers of known sex, tribe, and stated age; 10.5% of teeth were affected. Canines and first premolars were the most common teeth associated with dehiscences and fenestrae. Dehiscences occurred more commonly than fenestrae (1:0.49). The defects were found exclusively in the buccal plate of the alveolar process.     

The metabolism of abscisic acid in flacca,a wilty mutant of tomato

The wilty tomato mutant flacca and the normal variety Rheinlands Ruhm were used in this research. The mutant phenotype was explained mainly by hormonal changes. One of these, the decrease in abscisic acid level, was suggested as the hormonal change closest to the mutated gene. The cause of the lower abscisic acid level in the mutant, which may be enhanced breakdown or inactivation, or inhibited biosynthesis, was investigated. The first possibility was studied by comparing mutant and normal plants treated with t-abscisic acid-2-C¹⁴ for (1) rate of production of labeled methanol-extractable metabolites and (2) radioactivity remaining in the methanol-unextractable fraction. The level of trans, trans-abscisic acid relative to that of cis,trans-abscisic acid was studied in untreated plants. Only two radioactive regions containing metabolites of abscisic acid were detected from either of the plant types, and their rates of production relative to total radioactivity was equal. The radioactivity in the methanolunextractable fraction and the level of trans,trans-abscisic acid were very low in both mutant and normal plants. The second possibility was studied partly by comparing the levels of various xanthophylls in mutant and normal plants and their effect after illumination on cress seed germination. Xanthophylls of both plant types were identical in their absorption spectra, but their levels were higher in the mutant. Of these xanthophylls, illuminated neoxanthin inhibited seed germination in both plant types, but more effectively in the mutant. The most probable explanation for the low level of cis,trans-abscisic acid in flacca is that the conversion of farnesyl PiP to abscisic acid is inhibited in this plant.