Inhibition of Transformation of Bacillus subtilis by Heavy Metals

Mercuric ions, as well as organomercuric ions and cadmium ions, can inhibit deoxyribonucleic acid-mediated transformation in Bacillus subtilis 168 without decreasing the viability of the total population. Differences in the inhibition of transformation by mercuric ions are identifiable on a temporal and concentration dependence basis. Sensitivity to low concentrations (9.2 x 10(-8) M) appears early in the uptake of deoxyribonucleic acid before the transformed markers have become insensitive to deoxyribonuclease. Resistance to "low concentrations" of Hg(2+) is kinetically indistinguishable from the requirement for magnesium in the transformation process. This inactivation is not reversed by the mercury-binding compound glutathione. Sensitivity to mercuric ions at a higher concentration (5.52 x 10(-7) M) occurs after the donor deoxyribonucleic acid has become insensitive to deoxyribonuclease. These complex interactions between mercuric ions and the process of transformation are discussed.     

Polyamine Limitation of Growth Slows the Rate of Polypeptide Chain Elongation in Escherichia coli

The rate of polypeptide chain elongation during steady-state, polyamine-limited growth of a mutant of Escherichia coli was measured by two independent techniques. Analysis of polysome patterns gave values of 17.5 and 9.5 amino acids per s at 37 C in unstarved and polyamine-limited cells, respectively. From the kinetics of entry of labeled amino acids into polypeptides of defined molecular weights, values at 30 C of 10.1 and 5.8 amino acids per s were obtained for unstarved and polyamine-limited cultures, respectively. Correction of these values to 37 C resulted in rates of 15.0 and 8.7 amino acids per s. These results support the previous conclusion, based on the kinetics of beta-galactosidase induction, that polyamine starvation decreases the rate of protein synthesis by limiting the velocity of polypeptide chain elongation.     

Biogenesis of β-Carotene in Mycobacterium kansasii

The biogenesis of beta-carotene in the photochromogen Mycobacterium kansasii consists of two reactions. The first reaction is photochemical, and is dependent on the wavelength of the incident light and on oxygen but is independent of temperature. The second reaction does not require illumination, and is dependent on the temperature and on oxygen. The latter, or dark reaction, requires the synthesis of new protein, and was shown to have the characteristics of an inducible system. Carotenogenesis was stimulated by incident light of wavelengths of 420, 540, and 650 nm. Immediately after illumination there was an increase in the synthesis of ribonucleic acid and beta-carotene accumulation started after a lag of 8 to 10 min. The synthesis of beta-carotene exhibited temperature dependence with an optimum of about 36 C.     

Separate Branches of the uvr Gene-Dependent Excision Repair Process in Ultraviolet-Irradiated Escherichia coli K-12 Cells; Their Dependence upon Growth Medium and the polA, recA, recB, and exrA Genes

The extent of repair of single-strand breaks (incision breaks) induced in the deoxyribonucleic acid (DNA) of Escherichia coli K-12 cells by the uvr gene-dependent excision repair process after ultraviolet (UV) radiation was determined in the wild-type, polA1, recA56, recB21, and exrA strains. The wild-type strain repaired all incision breaks after incident doses of UV radiation (254 nm) of approximately 60 J m(-2) or less when incubated in growth medium, or approximately 15 J m(-2) or less when incubated in buffer. The polA1 strain repaired the incision breaks completely after incident doses of approximately 12 J m(-2) or less when incubated in growth medium, or after approximately 4 J m(-2) when incubated in buffer. The recA13, recB21, and exrA strains showed essentially complete repair after incident doses of 10 to 15 J m(-2) whether the cells were incubated in buffer or growth medium. These results suggest that the uvr gene-dependent excision repair process may be divided into two branches, one which is dependent on the presence of growth medium and also the rec(+)exr(+) genotype, and a second which can occur in buffer (growth medium-independent) and is largely dependent on DNA polymerase I. The presence of chloramphenicol in the growth medium resulted in an inhibition of the growth medium-dependent repair occurring in wild-type and polA1 cells and had little or no effect on the extent of repair observed in recA56, recB21, or exrA cells. The similarities between the growth medium-dependent and -independent branches of excision repair and two known processes for the repair of X-ray-induced single-strand breaks are discussed.     

Culture Medium for Enterobacteria

A new minimal medium for enterobacteria has been developed. It supports growth of Escherichia coli and Salmonella typhimurium at rates comparable to those of any of the traditional media that have high phosphate concentrations, but each of the macronutrients (phosphate, sulfate, and nitrogen) is present at a sufficiently low level to permit isotopic labeling. Buffering capacity is provided by an organic dipolar ion, morpholinopropane sulfonate, which has a desirable pK (7.2) and no apparent inhibitory effect on growth. The medium has been developed with the objectives of (i) providing reproducibility of chemical composition, (ii) meeting the experimentally determined nutritional needs of the cell, (iii) avoiding an unnecessary excess of the major ionic species, (iv) facilitating the adjustment of the levels of individual ionic species, both for isotopic labeling and for nutritional studies, (v) supplying a complete array of micronutrients, (vi) setting a particular ion as the crop-limiting factor when the carbon and energy source is in excess, and (vii) providing maximal convenience in the manufacture and storage of the medium.     

Bloom's syndrome. III. Analysis of the chromosome aberration characteristic of this disorder

The following hypothesis is put forward: X chromatin in man condenses around a center which is situated on Xq at a short distance from the centromere. The hypothesis is based on, and explains, two classes of observations. (1) Abnormal X chromosomes that have the assumed center in duplicate form bipartite Barr bodies in part of the cells. The frequency of bipartite bodies and the distance between the two parts seem to be determined by the distance between the postulated centers. (2) A large number of variously abnormal X chromosomes have been described. Almost all of them possess the postulated center and it seems possible that the very few apparent exceptions represent misidentifications of chromosome Xq — as isochromosome i(Xp). According to the hypothesis, chromosomes lacking the center would form no Barr body and therefore presumably would not be inactivated, thus leaving the cell severely unbalanced. Furthermore, absence of the center might interfere with the viability of the chromosome itself.     

Possible mode of action of a photosynthetic inhibitor produced byPandorina morum

The mode of action of the photosynthetic inhibitor produced byPandorina morum was examined by exposingVolvox globator and isolated spinach chloroplasts to a partially purified inhibitor preparation. Oxygen evolution ofVolvox, whole chloroplasts, and broken chloroplasts (-Calvin cycle) was reduced indicating that the substances inhibit the light reactions of photosynthesis. Oxygen evolution studies of other Volvocaceae confirmed the observation thatPandorina morum is not significantly influenced by its own inhibitor. Molecular weight approximation by gel filtration established that the inhibitor has a low, molecular weight (probably below 100 mw).     

Immune response genes in inbred rats. II. Segregation studies of the GT and GA genes and their linkage to the major histocompatibility locus

Genetic analysis of the high responder-non-(or low) responder differences between WF and ACI rats to the synthetic copolymers GT and GA established singleIr-genes for both antigens and dominance for high responder status.Ir-GT andIr-GA are linked to the major histocompatibility locus. It could be demonstrated that only T cells carrying the high responderIr-GT gene undergo in vitro blast transformation to GT. The advantages of the rat systems for further studies of the regulatory role ofIr-genes on the cellular level are discussed.Abbreviations cpm counts per minute - DHR delayed hypersensitivity reaction - GA random synthetic copolymer of L-glutamic acid⁵⁰, L-alanine⁵⁰, M.W. 45,000 - GT random synthetic copolymer of L-glutamic acid⁵⁰, L-tyrosine⁵⁰, M.W. 22,000 - Ir gene immune response gene - MLC mixed lymphocyte cultures - LDH lactic dehydrogenase - (T,G)-A-L branched chain synthetic polymer of poly-L (tyrosine, glutamic acid)-poly-D, L-alanine-poly-L-lysine Rat Strains ACI ACI/MaI - WF Wistar Furth - AUG August 28807/Cr     

Genetic control of the immune response in mice: V. Minor genes involved in the response to H-Y and Ea-1 antigens

Murine responses to both the male specific histocompatibility antigen H-Y and the erythrocyte alloantigen Ea-1 are regulated by genetic factors. In each case a single major gene that controls the immune response has been identified, but additional modifying factors can be demonstrated if appropriate strain combinations are studied. A single gene controlling the response to Ea-1 antigens, which segregates when strains YBR and B10.D2 are crossed, has been shown not to be an allele of theIr-2 locus. A new phenomenon has also been observed in the control of anti-Ea-1 antibody production in that the mating of two responding strains, YBR and HTG, produces an F₁ generation of complete nonresponders. By linkage tests it was shown that the responding strain HTG possesses the nonresponder allele at theIr- 2 locus, so there appear to be recessive genes in the background which are able to overcome the suppressive influence of this allele.