Conditional Mutator Gene in Escherichia coli: Isolation, Mapping, and Effector Studies

A mutator gene, mutD5, whose phenotype is conditional, has been identified in Escherichia coli. By P1 transduction it has been shown to lie at about 5.7 min on the chromosome, being co-transduced with proA and argF. In rich medium, streptomycin- and nalidixic acid-resistant mutation frequencies are 50 to 100 times higher than those in minimal medium. In minimal medium, the mutD5-induced mutation frequencies are still 50 to 100 times above co-isogenic wild-type (mut(+)) levels. Similar results were obtained with all markers tested. Mutant frequencies can be raised by thymidine in the medium at concentrations as low as 0.04 muM, or by the endogenous generation of thymidine from thymine plus a deoxyribosyl donor. Deoxyadenosine, various ribonucleosides, thymine, and 2-deoxyribose do not stimulate mutation. None of these effects are related to growth rate, since growth rate and mutation rate can be decoupled completely.     

Selection for High Mutation Rates in Chemostats

Complementation and polarity suppression data are interpreted in terms of the genetic structure of the maltose B region. It is proposed that this region comprises two divergent operons. One operon includes malK, a cistron involved in maltose permeation, and lamB the only known cistron specifically involved in lambda receptor synthesis. The other operon includes malJ(1) and malJ(2) which are most probably two different cistrons, both involved in maltose permeation*. It is further assumed that expression of the two operons is controlled by malT, the positive regulatory gene of the maltose system, located in the malA region. The target(s) for the action of the malT product is (are) most likely to be located between malJ(1) and malK. There is an indication that the two operons might overlap in the region of their promoters. The structure of such an overlap as well as the possible function of the products of the different cistrons in malB are briefly discussed.     

Esterases of Drosophila II. Biochemical Studies of Esterase-5 in D. pseudoobscura

In vitro enzyme hybridization was carried out with combinations of six allozymic variants of Esterase-5 from Drosophila pseudoobscura. Studies on heat stability and specific activity changes accompanying hybridization were done to examine the possible expression of overdominance at the biochemical level. In 11 of 15 combinations no significant change in specific activity was found following hybridization. In two cases hybridization resulted in a decrease in activity in the mixture, while in two cases esterase activity was elevated. Heat stability studies, in several cases, revealed reduced rates of inactivation in in vitro and in vivo heterozygotes compared with homozygotes. From these and other data a model for the molecular mechanism of heterosis is presented.     

Activity of phenol oxidases at the puparium formation stage in development of nineteen lozenge mutants of Drosophila melanogaster

Phenol oxidase activity of activated A₁ and A₂ (A₃) electrophoretic components from 19 lozenge mutant and three lozenge double mutant strains was compared to that of wild type flies. Melanin production by the activated A components with tyrosine as substrate was compared to activity in the same acrylamide gels with dopa as substrate. Melanin production decreased, first in the A₁ band and then in the A₂ (A₃) band, with increased morphological expression of the mutant genes. No melanin bands were obtained with either substrate in five of the more severely affected mutants. A possible correlation between phenol oxidase activity and quinone production necessary for normal development of eyes, female accessory sex organs, and claws is discussed.Supported by PHS grant AM-08331-05.     

Secondary and Tertiary Responses of the Induced Bactericidin from the West Indian Spiny Lobster, Panulirus argus

West Indian spiny lobsters, Panulirus argus, synthesized a hemolymph bactericidin after being injected with killed suspensions of gram-negative bacillus EMB-1 isolated from the normal gut of this lobster. To study differences between the primary response and secondary response, animals were given a primary antigen injection of EMB-1 followed by a second injection of the same antigen 22 to 51 days later. As a rule, secondary bactericidal responses were enhanced over the primary in a manner reminiscent of specific anamnesis in mammalian immunoglobulin synthesis. Immunological memory was also suggested when tertiary responses were compared to secondary and by the persistence of residual titers for many days or weeks without additional antigenic stimulation.     

Mutator Gene Studies in Escherichia coli

An Escherichia coli mutator gene, mutT, has been shown by P1-mediated crosses to map between the leucine and azide loci. The mutT1 and azi-r alleles cotransduce with a frequency of >92%. In mutT1/mutT⁺ merodiploids, the mutT1 phenotype is recessive; in mutT1/F′trp or mutT1/F′lac merodiploids, the mutT1 allele has a trans effect. The gene can mutate λ and T7 phage but not T1, T3, T4, T5, and S13.     

Cardiac muscle

Summary The ultrastructure of chicken and frog cardiac muscle are compared and then contrasted with the ultrastructure of mammalian cardiac muscle. Both chicken and frog cardiac muscle have no transverse tubules, remarkably few nexuses and no prominent M-lines. M-fibers of both animals are small (2–5 ) in diameter and contain dense granules. Chicken cardiac muscle like mammalian cardiac muscle has very well developed sarcoplasmic reticulum and couplings. The latter do not occur in frog cardiac muscle and the former is poorly developed in that muscle. Morphologic evidence is presented in the frog and chicken heart that would tend to attribute to the sarcoplasmic reticulum a transport function for electron-dense material (presumably proteinaceous) the possible significance of which is discussed. Purkinje fibers were identified in the form of a network on the endocardial surface of both atria and ventricles of chicken hearts. The topography of these fibers corresponds to that of a population of fibers in small mammalian hearts that, and unlike ventricular fibers in those animals, does not have transverse tubules.This investigation was presented, in part, at the 2nd Annual Summer Workshop of the Council on Basic Science of the American Heart Association in Mountain View, California, August 5–8, 1968; at the Gordon Conference on Myocardial Contractility in Holderness, New Hampshire, August 12–16, 1968; and at the 8th Annual Meeting of the American Society for Cell Biology in Boston, Massachusetts, November 11–13, 1968. This research was supported by grant No. 66737 from the American Heart Association, Inc. and by grant No. HE 08620 from the NIH.     

Specificity of the Induced Bactericidin of the West Indian Spiny Lobster, Panulirus argus

To investigate the specificity of an inducible hemolymph bactericidin, West Indian spiny lobsters were immunized with a variety of antigens. Bactericidal assays were conducted with strain EMB-1, a gram-negative bacillus isolated from normal lobster intestine. Animals given saline solution with or without 0.3% Formalin exhibited only a slight response similar to sham controls. Injections of type 2 pneumococci or bovine albumin produced slightly higher responses. These were much less pronounced than the homologous response to EMB-1. Formalin exhibited an adjuvant-like effect with EMB-1.     

Membrane changes in yeast cells caused by sulfhydryl reagents and accompanied by a selective release of sugar

Summary Iodoacetic acid or N-ethylmaleimide included in cell suspensions during measurements of sorbose exit from yeast cells caused sorbose efflux to occur at a uniform rate in contrast to the usual two-phase exit. Cells pretreated with these agents were still capable of sugar uptake, but the entire efflux now occurred at the usual initial rate. Microscopically, the vacuoles of treated cells were observed to be altered or disrupted. Vacuolar effects occurred before methylene blue was able to penetrate the external cell membrane and stain the cells. Vacuoleless cells also allowed a single rate of sorbose efflux. The selective effect upon intracellular membranes is interpreted as a disruption of the boundaries of an internal sugar compartment with the result that sugar exits from the cell at a rate controlled only by the external membrane.     

A stable mitomycin-induced LC-type albino mutant of Blastocladiella emersonii

In an effort to obtain orange mutants ofBlastocladiella emersonii Cantino &Hyatt, wild type zoospores were treated with mitomycin. From the variants produced, we obtained a stable, albino mutant (Ma-1) that differs significantly from another, previously described (Shaw &Cantino, 1969) UV-induced, albino variant. This report concerns the origin of Ma-1, its distinguishing features, and its apparent similarity to the few LC (late colorless) plants that normally appear in wild type populations. A preliminary note regarding mitomycin-induced variants ofB. emersonii has been published (Matsumae &Cantino, 1970).