Freeze-thaw-induced lateral transfer of non-conjugative plasmids by in situ transformation in <Emphasis Type="Italic">Escherichia coli</Emphasis> in natural waters and food extracts

Freeze-thaw treatment of condensed suspensions of mixed Escherichia coli strains in natural waters and food extracts caused in situ lateral transfer of non-conjugative plasmids. This phenomenon also occurred in distilled water and LB broth, and after 1–2 months of preservation at −20°C. The sensitivity of lateral transfer towards DNase activity suggested the involvement of in situ transformation. There were no clear correlations between transformation frequency and the chemical characteristics (Ca²⁺, Mg²⁺, and pH) of the samples. These results suggest the possibility that freeze–thaw-induced lateral gene transfer between bacterial cells occurs in natural and human environments.     

A Relationship between Papaincatalyzed Aminolysis of Ethyl Hippurate by Amino Acid Esters and Their Incorporation into Ovalbumin Hydrolysate during the Plastein Reaction

The effects of the colloidal properties of emulsion particles and the conformation of tryptic digests of soybean glycinin, the emulsifiers, on emulsion properties were investigated. The digests were separated into some fractions, and the properties of intact glycinin, two kinds of the best were examined. The diameter of the emulsion particles measured by spectroturbidimetry was not very different among the best emulsifiers and intact glycinin in spite of the difference in emulsifying ability; however, a new parameter, flocculation strength, which is the rigidity of the flocculated structure and is defined as the minimum detergent concentration for the dissociation of flocculation, closely and negatively related to the short term emulsion stability. The amount of adsorbed protein on the surface of the emulsion particles was also related to the long term emulsion stability. The two best emulsifiers were analyzed by gel filtration and circular dichroism. The emulsifiers contained large molecular components whose molecular weight and secondary structures were similar to intact glycinin. The conformational stability of the emulsifiers was evaluated by the change in emission maxima of the intrinsic fluorescence of the proteins against changing urea concentration, and the surface hydrophobicity of the proteins was estimated by the binding of l-anilino-8-naphthalene sulfonate (ANS). The emulsion stability increased with decreasing conformational stability and increasing surface hydrophobicity of the emulsifier proteins.     

Additional genes essential for replication of the mini-F plasmid from origin I

Summary We isolated a series of Tn5-insertional mutants from the mini-F plasmid, which has a deletion in the origin II region and replicates exclusively from origin I, and found that the mutants that had Tn5 in either the F4 or the F5 gene were defective in their replication. It is concluded that, in addition to the F3 gene on which we have reported previously, both the F4 and the F5 genes are essential for the replication from origin I.     

Fructose-diphosphate aldolase of Horseshoe crab (Tachypleus tridentatus).

Fructose-diphosphate aldolase [ED 4.1.2.13] was isolated from horseshoe crab ( living fossil) muscle and some molecular and enzymatic properties were examined. The enzyme was a tetramer with a molecular weight of about 160,000. The enzyme activity was inhibited by reduction with borohydride in the presence of the substrate and was inactivated by carboxypeptidase A [EC 3.4.12.2] digestion. The pH optima for fructose-diphosphate (FDP) and fructose-1-phosphate (F1P) activities were 6.5--8 and 7.5--8.2, respectively. The ratio of FDP/F1P activities was 30 and Km values were 1.7 times 10- minus 5 M and 2.5 times 10- minus 3 M, respectively, for the two substrates. The horseshoe crab aldolase was classified as class 1, type A, based on the results obtained. Extensive homology in various properties of the enzyme was observed when it was compared with enzymes from other sources, though some differences could be found in the amino acid composition and in the kinetic properties.     

Establishment of a novel embryonic stem cell line by a modified procedure

To generate mutant mice, embryonic stem (ES) cells are used as a vehicle for introducing mutations. The establishment of ES cells is diffucult because it requires specific skills and it is time-consuming. We established a novel ES cell line derived from hybrid mice between C57BL/6 and DBA/2 using a modified method. To collect a large number of preimplantational embryos, we collected embryos at the 8-cell stage and cultured them to blastocysts, whereas the usual procedure of preparing the delayed blastocysts demands technical skills. To eliminate unnecessary female cells at an initial stage of inner cell mass culture, male clones were selected by polymerase chain reaction to detect the mouseSry gene. The established ES cell line efficiently contributed to the germ-line when injected into 8-cell embryos of ICR mice. This potency was maintained after manipulation throughout gene targeting.Abbreviations DMEM Dulbecco's modified Eagle's medium - FBS fetal bovine serum - FIAU 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-iodouracil - LIF leukemia inhibitory factor - NEAA non-essential amino acids