Saul Yankofsky

Tel Aviv University | TAU · Microbilogy

Disparate gamma-subdivision proteobacteria artificially endowed with the same ice gene of enteric origin acquired water-freezing potential at -12 degrees C, but expressed it to varying extents under identical conditions of culture as well as after being subjected to certain post-culture treatments. Varying rates of cell-bound ice nucleus synthesis...

Two types of biotinylated cellulose disks were examined: filter-paper disks to which biotin had been covalently attached directly to the paper surface (biotinylcellulose) and disks on which biotin was attached to polyacrylamide side-chains grafted onto the filter-paper surface (biotinylpolyacrylamide-cellulose). The amount of avidin taken up from s...

Both gram-positive and gram-negative bacteria become excellent condensation nuclei when lyophilized to dryness. The same freeze-dry procedure does not inactivate the highly effective freezing nuclei produced by ice nucleation active bacteria. Therefore, irrespective of their contact nucleation potential, ice nucleation-active bacteria ought to effe...

This chapter describes the solid-phase assay for d-biotin and avidin on cellulose disks. Most biotin assay procedures exploit the absolute growth requirement of certain bacterial and yeast strains for d-biotin, or depend on the extremely high affinity of avidin for this vitamin. The binding assays, particularly those employing immobilized avidin, a...

Droplets freely suspended in the air stream of a wind tunnel were nucleated with dedicated bacterial cells in either the contact or immersion mode. Immersion freezing seemed to give a noncontinuous frequency distribution of freezing with temperature whereas the corresponding curve for contact was monotonic. Although the latter nucleation mode was m...

The normally very low frequency of ice nucleation-active individuals in populations of Bacterium M1 could be raised as high as 100% by treatments having perturbation of cellular DNA metabolism as their common denominator. The process whereby inactive cells acquired efficient freezing nuclei after induction was shown to require ongoing synthesis of...

Genetic transformation of Thiobacaillus thioparus auxotrophs to prototrophy was obtained at frequencies of up to 10(-2) when proliferating cell populations were exposed to chromosomal DNA from a nutritionally independent strain of the same bacterium. The rate at which transformation occurred depended on recipient growth rate and could be drasticall...

The dominant cytochrome in thiosulphate-grown Thiobacillus A2 was found to be of the c-type with a reduced or-band at 548 nm (c548). This c548 component did not constitute an integral part of the membrane carrier system. It did, however, appear to be part of a large complex not tightly bound to membranes. Reconstitution experiments showed that cyto...

Bacteria. The nalidixate-resistant (nax) mutant of Thiobacillus A2 used throughout these studies was obtained by plating a large number (> lo9) of cells on nutrient agar containing nalidixic acid (50 pg ml-l) and further purifying one of the several colonies which spontaneously arose after several days at 30 "C. This mutant, henceforth referred to...

Filter-paper disks of uniform size were chemically modified by the introduction of isonitrile functional groups. Avidin was then covalently linked to the disks in a four-component condensation reaction involving disk isonitrile groups and avidin carboxyl groups in the presence of a water-soluble aldehyde and an amine. Quantitative assay of unknown...

A method for the isolation of amino acid auxotrophs of Thiobacillus thioparus is described. Characterization of a leucine auxotroph indicated that leucine biosynthesis in T. thioparus was not different from that of heterotrophic bacteria. T. thioparus cells accumulated amino acids via an active mechanism. Kt values of amino acid transport were betw...

Amino acid transport in amino acid auxotrophs of Thiobacillus thioparus was enhanced during growth on rate-limiting amino acid concentration. A pleiotropic mutation enhanced general amino acid transport as manifested by higher values of Vmax of amino acid transport. Affinity constants remained unaltered. Mutants with enhanced transport properties d...

Freezing spectra of INA bacteria from different parts of the world were compared. A slight increase in efficiency of freezing nuclei produced by strains from warmer climates was observed. Whole cells of the most efficient strain produced nuclei active at temperatures ranging from 2 to 10°C, whereas fragments from these cells exhibited activity only...

Two distinct bacteria capable of freezing nucleus activity at temperatures as warm as –2.5C were repeatedly isolated from citrus and avocado plants in Israel. Phage typing has shown them to be related to each other and to one of the two groups of ice-nucleation-active bacteria already described by other workers. Evidence suggesting that these organ...

ColE1amp plasmids carrying the entire bio gene cluster were constructed in vitro using ColE1amp as the cloning vehicle and a lambda transducing phage, lambdaatt2, as the source of bio DNA. Restriction endonuclease EcoRI digests of ColE1amp and lambdaatt2 DNA were joined by polynucleotide ligase and plasmids bearing the entire bio gene cluster were...

In the absence of substrate oxidation, membrane vesicles of M. phlei were shown to accumulate proline, glutamine, and glutamic acid mediated by Cu2+. The Cu2+-mediated uptake of amino acids was found to be an active process and required the presence of amino acid binding protein(s). Thus, membrane vesicles which lack active transport of a particula...

Membrane vesicles of M. phlei actively take up proline in the absence of exogenously provided electron donors. Evidence is provided that endogenous transport is coupled to the oxidation-reduction of low-potential electron carriers, but does not involve the cytochromes. The endogenous transport was found to be enhanced under either aerobic or anaero...

It has been reported that the 16-S and 23-S components of Escherichia coli ribosomal RNA compete for common hybridization sites on homologous DNA. We here show that no such competition phenomenon occurs. Carefully purified preparations of the two major ribosomal RNA types do not competitively interact with one another during hybridization to Escher...

Reported here are experiments showing that the multiple cistrons coding for the 23-S component of ribosomal RNA in Escherichia coli are not arranged as a single, contiguous block of genes. Instead, it is probable that a gene for 16-S ribosomal RNA is in close physical proximity to every individual 23-S ribosomal RNA locus. Moreover, interspersed be...