Evolution of the mitochondrial DNA control region in the mbuna (Cichlidae) species flock of lake Malawi, East Africa

Considerable controversy has surrounded the application of mitochondrial DNA data to reconstruction of evolutionary relationships among the endemic cichlids of Lake Malawi. Central to this debate has been the issue of whether lineage sorting is complete, and thus whether these data actually reflect species phylogeny, or simply gene genealogy. Review of all mtDNA control region sequences available for members of one monophyletic subset of this species flock, the Malawi rockfishes, or mbuna, strongly indicates that lineage sorting is incomplete: Character-based analyses of these sequences reconstruct gene, not species, interrelationships. Analysis of the pattern of nucleotide substitutions differentiating these mtDNA alleles suggests that pyrimidine residues undergo transition substitutions more often than do purines. Estimation of the magnitude of derived sequence differentiation in light of the reconstructed gene genealogy suggests that the mbuna may be of considerably more recent vintage than previous molecular characterizations have indicated. Received: 6 April 1996 / Accepted: 3 March 1997     

Lectin recognition of host-like saccharide motifs in streptococcal cell wall polysaccharides

Viridans streptococci that participate in the microbial colonizationof teeth have cell wall polysaccharides composed of linear phosphodiester-linkedhexa- or heptasaccharide repeating units, each containing ahost-like disaccharide motif, either Galß1     

Recovery of intestinal membrane binding sites for K88 E. coli from pig mucosal organ cultures

Summary Putative receptors for K88+ E. coli from piglet intestinal epithelium were released into the organ culture medium and were demonstrated by direct binding with K88+ E. coli through the utilization of an in vitro binding procedure or by immunoprecipitation with K88 antigen.Incorporation of ¹⁴C-glucosamine by newborn to day old and 3-week to 6-week old piglet jejunal and ileal mucosa, in organ culture, occurred throughout the 24 hr culture period. Uptake in both age groups and both areas of the intestine was similar with a somewhat greater incorporation by the older age group.Secretion of ¹⁴C-glucosamine-labeled components into the culture medium was demonstrated by gel filtration of the concentrated medium. Some large molecular weight components eluted in the void volume in excess of 2 x 10⁶ daltons. A second peak of activity was spread from approximately 690K to 25K daltons. All eluted fractions demonstrated binding to K88+ E. coli.Antibodies to purified brush borders from susceptible pigs produced prominent precipitation bands following double diffusion with concentrated organ culture media which confirmed that the organ culture media contained labeled proteins of brush border origin.Immunoprecipitation of the intestinal mucosal organ culture media with K88+ pili and pilus antisera, followed by electrophoresis with SDS and reduced conditions, demonstrated a subunit of approximately 35K daltons.     

Dual nucleotide specificity of bovine glutamate dehydrogenase. The role of negative co-operativity.

The thionicotinamide analogues of NAD+ and NADP+ were shown to be good alternative coenzymes for bovine glutamate dehydrogenase, with similar affinity and approx. 40% of the maximum velocity obtained with the natural coenzymes. Both thionicotinamide analogues show non-linear Lineweaver-Burk plots, which with the natural coenzymes have been attributed to negative co-operativity. Since the reduced thionicotinamide analogues have an isosbestic point at 340nm and have an absorption maximum at 400nm, it is possible to monitor reduction of natural coenzyme and thionicotinamide analogue simultaneously by dual-wavelength spectroscopy. When glutamate dehydrogenase is presented with NADP+ and thio-NADP+ simultaneously, the enzyme oligomer senses saturation of its coenzyme-binding sites irrespective of the exact nature of the coenzyme and locks the oligomer into its highly saturated form even when low saturation of the monitored coenzyme is present. These experiments substantiate the suggestion that glutamate dehydrogenase shows negative co-operativity in its catalytically active form.     

Production and Biological Activity of Secalonic Acid D

Twenty isolates of Penicillium oxalicum produced secalonic acid as their major secondary metabolite. Fermentation conditions were determined for toxin production in grain and liquid media. The 50% lethal dose value for mice ranged from 26.5 to 51.7 mg/kg dependent on animal strain and sex, males being more susceptible than females. Secalonic acid was nontoxic and nonteratogenic to the chicken embryo and exhibited poor antibiotic properties. Its potential role in mycotoxicoses is discussed.     

Amber mutations in Escherichia coli essential genes: isolation of mutants affected in the ribosomes.

Summary A method to obtain amber mutations in ribosomal protein genes is described. It relies on the P1-mediated localized mutagenesis (Hong and Ames, 1971) and on the fact that the recipient strain contains (a) an efficient but genetically unstable suppressor, (b) a particular thermoinducible prophage which kills suppressor hosts at 42° C. Exposure of these bacteria to the high temperature yields frequent suppressor-free derivatives while none will be found if the strain carries an amber mutation in an essential gene. Eleven mutants have been isolated by this method, of which at least six appear to carry amber mutations. All of them map close to, and to the right of spcA, in a region which codes mostly for ribosomal proteins. Three mutants were studied biochemically; all three show defective ribosomal assembly in vivo upon loss of suppression.     

Regeneration of masseter muscle following lidocaine-induced degeneration. A histochemical study.

The histoenzymatic characteristics of regenerating myofibers of rat masseter muscle following injection of 1% lidocaine, as well as morphometric and histochemical characteristics of the typical myofibers, were investigated. Myoblasts appeared initially by day 1 among numerous macrophages within the confines of degenerating myofibers. Myotubes predominated by the 3rd day. Complete regeneration of the muscle occurred by at least 45 days. Phosphorylase activity was absent at day 1 and reappeared by the 5th day when the regenerating myofibers showed slight activity. By the 15th day the myofiber types had partly differentiated; red myofibers were smaller and stained less intensely than the white myofibers. Myotubes stained uniformly for succinic dehydrogenase activity from 3 until 5 days. After 5 days this staining increased gradually. Myofiber types began differentiation by 15 days and were fully differentiated by 45 days. ATPase activity was barely evident by 1-3 days. This activity appeared uniformly low up to 5 days and increased to an intensity comparable with that of the typical myofiber by 15 days. Slight leucine aminopeptidase activity occurred in macrophages 1 day following injection. By 3 days this activity appeared in the remaining myoblasts and in the myotubes. Some activity was found in the fibroblasts. This staining intensity at 5 days was equal to that of earlier lesions. A trace of this activity was found at 7 days, and none at 15 days. Glucose-6-phosphate dehydrogenase activity was present in the macrophages by day 1. It increased by 3 days and occurred mainly in myoblasts and myotubes. This activity decreased by 5 days, and none was found by 7 days.