Isolation and characterization of DNA repetitions carrying the chromosomal beta-lactamase gene of Escherichia coli K-12.

Summary A ColE1 hybrid plasmid, pNU1, carrying the amp operon coding for chromsomal -lactamase was isolated from the Clarke and Carbon collection and physically mapped. The physical location of ampC within this plasmid was further deduced by in vitro cloning.By reciprocal recombination between pNU1 and chromosome of two unstable -lactamase hyperproducing E. coli K-12 mutants a large plasmid from each mutant was obtained. The respective plasmid was physically mapped and found to contain five and two repeated DNA segments. The repetitions within each plasmid were equal in size, 9,800 bp and 11,900 bp respectively and were organized in tandem. The end points of the repeats were different in the two plasmids but shared a DNA segment carrying the ampC gene. The chromosomal DNA of the -lactamase hyperproducing E. coli mutants were found to contain an amplified DNA segment equal in size to the repeated unit found in the respective plasmid. The data shows that up to 10 identical repeats organized in tandem can be generated by a normal mutation frequency in E. coli.     

Nitrous acid mutagenesis of duplex DNA as a three-component system.

Purified native Hemophilus influenzae DNA is relatively insusceptible to nitrous acid (NA) mutagenesis in vitro, but is readily mutated following denaturation. NA mutagenicity for duplex DNA is significantly increased in the presence of various alcohols, glycols, phenols or primary amines. Phenol-extracted DNA contains dissociable contaminants of low molecular weight that enhance NA mutagenesis. Enhancement of NA mutagenesis by phenol and by spermine is due to the formation of unstable molecular species. We propose that reactive organic nitroso compounds are formed which then serve as delivery vehicles to promote mutagenicity of native DNA, perhaps via transnitrosation reactions. Similar reactions probably occur in vivo to promote NA-induced base substitution (but not frameshift) mutations in Salmonella typhimurium and in Escherichia coli. The possible significance of these observations to carcinogenesis is discussed.     

Spectral properties of heavily glaucous and non-glaucous leaves of a succulent rosette-plant

Summary Comparisons of reflection, transmittance, and absorptance spectra of heavily glaucous leaves, glaucous leaves from which the glaucescence was experimentally removed, and naturally occurring non-glaucous leaves of a single species (Dudleya brittonii Johansen) reveal that glaucescence, a powdery wax coating on the leaf surface, is responsible for very high reflectance of ultraviolet radiation (UV) and high reflectances of visible and near-infrared radiation. UV reflectance (up to 83% in UV-B) measured for glaucous leaves of D. brittonii, a succulent rosette-plant occurring in fissures in steep volcanic outcrops, is higher than that reported for any other plant species. Non-glaucous leaves of the species reflect about 10% in UV. I hypothesize that the high UV reflectance of glaucous leaves is ecologically significant in reducing damage to dehydrated leaves from visible and UV-B radiation, thus promoting longevity of the leaves important both in conservation of the mineral nutrient capital of these succulent plants and in their acquisition and storage of water. This and other demonstrated and hypothesized functions of glaucescence are discussed in terms of the evolutionary significance of glaucescence in succulent plants.     

Bacterial feeding by the rotifer Brachionus calyciflorus: Clearance and ingestion rates,behavior and population dynamics

Summary The rotifer Brachionus calyciflorus is capable of collecting and ingesting cells or short chains of a laboratory-grown bacterium Aerobacter aerogenes. Clearance rate, the volume of water effectively processed animal ^-1h^-1, does not vary systematically with bacterial density between 0.01 and 100 g dry weight ml^-1. Consequently, ingestion rates are strongly density-dependent, reaching maximal values at the highest food densities tested. Bacterial feeding rates are consistently lower than those determined with larger food types, except in very dense cell suspensions. A. aerogenes in high concentration (100 g ml^-1) induces Brachionus to orient their pseudotrochal cirri to form screens over the buccal funnel; this behavior is at least four times less frequently observed at low (10 g ml^-1) food density. Despite its occurrence, pseudotrochal screening appears ineffective in regulating bacterial ingestion rate. B. calyciflorus can be cultured xenically for greater than 40 generations fed A. aerogenes alone, with no diminution in net reproductive rate or intrinsic rate of natural increase, and no lengthening in cohort generation time.     

Ultrastructural and autoradiographic study of the intranuclear inclusions of Pinguicula lusitanica L.

Intranuclear inclusions are found in Pinguicula lusiaanica. Observations with an electron microscope equipped with a goniometric stage demonstrate that they are formed with numerous similarly oriented lamellae. Enzyme digestions of ultrathin sections show that the inclusions are composed of protein. An autoradiographic study, after incubation of pieces of leaves or roots in a physiological medium containing tritiated arginine, shows that the inclusions grow in tissue incubated in such an artificial mineral medium.     

The behavior of a group of captive pygmy chimpanzees (Pan paniscus)

A group of captive pygmy chimpanzees (Pan paniscus) was studied in the San Diego Zoological Gardens. The behavior patterns that these animals exhibit are described. Each of these behavior patterns is compared to those described for wild and captive common chimpanzees (P. troglodytes). Differences in behavior between these two species are attributed to specialization of the pygmy chimpanzee to a rain forest habitat and to a monogamous social system.     

On the ecology and behavior ofCebus albifrons in eastern Colombia: II. Behavior

A 503-contact-hr study of a 35 member group ofCebus albifrons was conducted in eastern Colombia in 1977 and 1978. The reactions of the group often centered on the largest adult male, which seemed dominant over all other members of the group. This “alpha” male reacted to perceived danger by putting himself between the group and the danger where he threatened and observed until the other members left the scene. Many members of the group sought the alpha's physical support while using threatening behaviors. Much tolerance towards juveniles and infants was shown by adult and subadult males which included carrying young animals out of danger. Territorial behavior was observed towards neighboring groups. Many behaviors were similar to other species ofCebus.     

Specific localization of 2′,3′-cyclic nucleotide 3′-phosphohydrolase, (Ca/Mg)-ATPase, and acetylcholinesterase in human erythyrocyte membrane

A procedure was developed for the detection of 2′,3′-cyclic nucleotide 3′-phosphohydrolase in myelin. This assay was sufficiently sensitive to detect the low levels of 2′,3′-cyclic nucleotide 3′-phosphohydrolase in human erythrocytes. The 2′,3′-cyclic nucleotide 3′-phosphohydrolase of human erythrocytes was determined to be exclusively associated with the inner (cytosolic) side of the membrane. Leaky ghostsand resealed ghosts were assayed for 2′,3′-cyclic nucleotide 3′-phosphohydrolase, (Ca²⁺/Mg²⁺-ATPase, and acetylcholinesterase activity, and the 2′,3′-cyclic nucleotide 3′-phosphohydrolase profile is the same as that of the (Ca²⁺/Mg²⁺)-ATPase, an established inner membrane maker.     

Partial purification and characterization of nitrous oxide reductase fromParacoccus denitrificans

We report the first partial purification of nitrous oxide reductase, a unique and labile enzyme of denitrifying bacteria. The procedure, which required anaerobic conditions throughout, resulted in a 60-fold purification relative to crude lysate in the case ofParococcus denitrificans. The molecular weight was estimated by gel exclusion chromatography to be about 85,000. The partially purified enzyme is inactivated rapidly by O₂, dithionite, and mercaptoethanol and is reversibly inhibited by moderate concentrations of common salts. Up to 80% of the original activity can be reconstituted following O₂ inactivation by incubating the enzyme with reduced benzyl viologen for 2 to 3 h. TheV _max pH profile shows a broad maximum at pH 8. The enzyme is irreversibly retained by common anion exchangers in the range pH 7 to 8 but can be eluted in acceptable yield as one of the last components from an imidazole-based anion exchange material by means of a pH gradient. This behavior implies that nitrous oxide reductase is very acidic. Among the several peptides observed by sodium dodecyl sulfate slab electrophoresis, only two, with apparent molecular weights of 58,000 and 25,000, correlated closely with the activity of fractions eluted from the imidazole column. These two peptides together comprised about 30% of the total protein in the fractions with highest specific activity.