Multiple independent origins of mitochondrial gene order in birds

Mitochondrial genomes of all vertebrate animals analyzed to date have the same 37 genes, whose arrangement in the circular DNA molecule varies only in the relative position of a few genes. This relative conservation suggests that mitochondrial gene order characters have potential utility as phylogenetic markers for higher-level vertebrate taxa. We report discovery of a mitochondrial gene order that has had multiple independent originations within birds, based on sampling of 137 species representing 13 traditionally recognized orders. This provides evidence of parallel evolution in mitochondrial gene order for animals. Our results indicate operation of physical constraints on mitochondrial gene order changes and support models for gene order change based on replication error. Bird mitochondria have a displaced OL (origin of light-strand replication site) as do various other Reptilia taxa prone to gene order changes. Our findings point to the need for broad taxonomic sampling in using mitochondrial gene order for phylogenetic analyses. We found, however, that the alternative mitochondrial gene orders distinguish the two primary groups of songbirds (order Passeriformes), oscines and suboscines, in agreement with other molecular as well as morphological data sets. Thus, although mitochondrial gene order characters appear susceptible to some parallel evolution because of mechanistic constraints, they do hold promise for phylogenetic studies.     

Evaluation of bleached kraft mill process water using Microtox(R), Ceriodaphnia dubia, and Menidia beryllina toxicity tests

We show herein that human DNA topoisomerase II beta is functional in yeast. It can complement a yeast temperature-sensitive mutation in topoisomerase II. The effect on human topoisomerase II beta of a number of topoisomerase II inhibitors was analysed in a yeast in vivo system and compared with that of human topoisomerase II alpha and wild-type yeast topoisomerase II. A drug permeable yeast strain (JN394 top2-4) was used to analyse the in vivo effects of known anti-topoisomerase II agents on human topoisomerase II beta transformants. A parallel analysis on human topoisomerase II alpha transformants provides the first in vivo analysis of the responses of yeast bearing the individual isoforms to these drugs. The strain was analysed at 35 degrees C, a non-permissive temperature at which only plasmid-borne topoisomerase II is active. A shuttle vector with either human topoisomerase II beta, human topoisomerase II alpha or yeast topoisomerase II under the control of a GAL1 promoter was used. The key findings were that amsacrine produced comparable levels of cell killing with both alpha and beta, whilst etoposide, doxorubicin and mitoxantrone produced higher degrees of cell killing with alpha than with beta or yeast topoisomerase II. Merbarone had the greatest effect on the yeast strain bearing plasmid-borne yeast topoisomerase II. Suramin, quercetin and genistein showed little cell killing in this system. This yeast in vivo system provides a powerful way to analyse the effects of anti-topoisomerase II agents on transformants bearing the individual human isoforms. This system also provides a means of analysing putative drug-resistance mutations in human topoisomerase II beta or to select for drug-resistance mutations in human topoisomerase II beta.     

Reactions of diaminoalkanes with bismaleimides: Synthesis of some unusual polyimides

Michael additions of the secondary diamines N,N′-dimethyl-1,6-hexanediamine ( 14 ) or piperazine to the electrophilic carbon–carbon double bonds of N,N′-bismaleimido-4,4′-diphenylmethane ( 2 ) or N,N′-bismaleimido-1,8-octane ( 4 ) afford four unusual, high-molecular-weight (η_inh = 0.49–2.16 dL/g) polyimides ( 10 – 13 ). The most interesting of these, polymer 12 (the product of 4 and 14 ), is a tough elastomeric resin with a glass transition temperature (T_g) near 0°C; in contrast, 10, 11, and 13 exhibit T_g >86°C. Freshly prepared 12 is soluble and thermoplastic ( 12 is readily compression molded at 110°C), but the bulk polymer crosslinks slowly under ambient laboratory conditions and eventually (48 days) becomes insoluble, while 10, 11, and 13 remain soluble indefinitely. Along with further comparisons of the properties of 10 – 13 , details of the synthesis and characterization of these new polyimides are described. Also discussed are reactions of bismaleimide 2 with 1,6-diaminohexane, which unlike the formation of linear 10 – 13 , generate crosslinked, insoluble products.