Insertional inactivation of a gene which controls expression of vancomycin resistance on plasmid pHKK100

Expression of inducible high level vancomycin resistance (Vmr) in enterococci appears to require other plasmid-encoded genes in addition to the previously described structural genes vanA and vanH. Tn917 mutagenesis was used to identify such a region in the Vmr plasmid pHKK100. Insertional inactivation of a 693-bp open reading frame upstream from vanH resulted in complete loss of Vmr. This putative 26,642-Da protein has been designated VanR.     

Metabolism of nitric oxide and nitrous oxide during nitrification and denitrification in soil at different incubation conditions

Abstract NO production and consumption rates as well as N₂O accumulation rates were measured in a loamy cambisol which was incubated under different conditions (i.e. soil moisture content, addition of nitrogen fertilizer and/or glucose, aerobic or anaerobic gas phase). Inhibition of nitrification with acetylene allowed us to distinguish between nitrification and denitrification as sources of NO and N₂O. Under aerobic conditions untreated soil showed very low release of NO and N₂O but high consumption of NO. Fertilization with NH₄⁺ or urea stimulated both NO and N₂O production by nitrification. Addition of glucose at high soil moisture contents led to increased N₂ and N₂O production by denitrification, but not to increased NO production rates. Anaerobic conditions, however, stimulated both NO and N₂O production by denitrification. The production of NO and N₂O was further stimulated at low moisture contents and after addition of glucose or NO₃⁻. Anaerobic consumption of NO by denitrification followed Michaelis-Menten kinetics and was stimulated by addition of glucose and NO₃⁻. Aerobic consumption of NO followed first-order kinetics up to mixing ratios of at least 14 ppmv NO, was inhibited by autoclaving but not by acetylene, and decreased with increasing soil moisture content. The high NO-consumption activity and the effects of soil moisture on the apparent rates of anaerobic and aerobic production and consumption of NO suggest that diffusional constraints have an important influence on the release of NO, and may be a reason for the different behaviour of NO release vs N₂O release.     

Construction of a new universal vector for insertional mutagenesis by homologous recombination

We describe here the construction of a vector (pSSC-9) which can be used for the insertional mutagenesis of any gene for which genomic sequences have been cloned. This vector contains a neomycin-resistance-encoding gene (neo^R) which is driven by a modified thymidine kinase (tk) promoter for positive selection. Flanking neo^R are two tk genes driven by their own promoters for negative selection of nonhomologous insertions. The neo^R and tk cassettes are separated by four unique cloning sites on the right-hand side of the neo^R cassette and three unique sites on the left-hand side. The vector also includes two SfiI sites, one on each side of the tk cassettes, for the excision of the cloned genomic DNA fragments along with the selectable markers. Electroporation of pSSC-9 into mouse embryonic stem (ES) cells and cultured diploid mouse adrenal Y-1 cells conferred resistance to G418 and sensitivity to ganciclovir in both cell lines. These results illustrate the expression of the positive and negative selectable markers in two different cell lines and thus suggest that the vector could be used in ES cells, as well as in cultured somatic cells.     

The role of visual cues in the facilitation of growth in a schooling fish

Synopsis This study tested the hypothesis that visual contact between fish may result in enhanced rates of growth in a schooling fish. Juvenile chum salmon, Oncorhynchus keta, were held singly and reared in isolation or in visual contact with conspecifics. Fish were fed at either a low (6% body weight d^–1) or high (20% body weight d^–1) ration for 42d. Specific rates of weight gain were 18% greater at low ration and 38% greater at high ration for fish in visual contract with conspecifics than for those held in isolation. The results demonstrate a selective advantage of visual cues associated with schooling behavior and suggest that the efficacy of growth models for schooling fishes may be enhanced by the consideration of social interactions which may facilitate growth.     

Photosynthetic capacity in microalgae associated with Antarctic pack ice

Summary Previous studies of primary production in Antarctic seas have concluded that microalgae associated with sea ice make only a minor contribution to the carbon budget; however, production estimates for sea ice algae have been based almost exclusively on microalgae from nearshore fast ice. We measured biomass and rates of photosynthesis (at saturating irradiances) in microalgae collected from offshore pack ice during four cruises to the Weddell-Scotia Sea and the region west of the Antarctic Peninsula. Chlorophyll a concentrations in pack ice (0.089 to 260 g 1^-1) were as high as reported from fast ice. Photosynthetic rates typically ranged (median 75%) from 0.3 to 3.6 C g chl a ^-1 h^-1 (n=127; arithmetic mean = 1.7, S D =1.9). These photosynthetic capacities are approximately an order of magnitude greater than previously reported for fast ice microalgae, but are similar to rates reported for Antarctic phytoplankton. Because pack ice constitutes more than 90% of the ice cover in Antarctic seas and indigenous microalgae have a higher photosynthetic capacity than previously realized, we raise the question: has the importance of sea ice algae to primary product: on in the southern ocean been underestimated?     

A nomenclature for the genes encoding the chlorophylla/b-binding proteins of higher plants

We propose a nomenclature for the genes encoding the chlorophylla/b-binding proteins of the light-harvesting complexes of photosystem I and II. The genes encoding LHC I and LHC II polypeptides are namedLhca1 throughLhca4 andLhcb1 throughLhcb6, respectively. The proposal follows the general format recommended by the Commision on Plant Gene Nomenclature. We also present a table for the conversion of old gene names to the new nomenclature.     

CONGRUENCE BETWEEN SUPERPOSITIONAL AND PHYLOGENETIC PATTERNS: COMPARING CLADISTIC PATTERNS WITH FOSSIL RECORDS

Abstract— As the only direct evidence of past organismic history, the fossil record has always figured importantly in the reconstruction of phylogeny. But the incomplete nature of the fossil record has also been cited as a basis for claiming that fossils play only a secondary role in developing phylogenetic hypotheses that encompass extant taxa. The reliability of fossil data in such applications is a function of the degree of fit between superpositional relationships and the sequence of phylogenetic events. Thirty-eight vertebrate cases are examined for the fit between age data based on fossil first occurrences and phylogenetic results based on cladistic analysis. A general correspondence between superpositional and cladistic information is observed, although the degree of fit varies widely among cases. Horses, certain other ungulates, synapsids and basal archosaurs, which show very high correlations, are taxa characterized by an abundance of superpositional and cladistic data. Other groups, such as primates, show very poor correlations because certain major clades have either unreasonably short fossil durations or no fossil record at all. Correlations are also diminished when either fossil records or cladistic sequences are poorly resolved. In most cases, cladistic resolution was observed to exceed superpositional resolution. Correlations can be enhanced by more precise (e.g. radiometric) age dates, but these also place a high expectation on the fit between fossil first occurrence and cladistic results. Stratigraphic occurrence does not always provide a precise reflection of independently derived phylogenies, but the correspondence between age and cladistic information is remarkably high in a notable number of vertebrate examples.     

Localization of the gene for a third G protein β-subunit to mouse chromosome 6 near Raf-1

The large family of signal transducing proteins known as G proteins are heterotrimers that dissociate into an independent α-subunit and βγ-subunit complex after ligand binding or other stimulation. For Gα, at least 30 distinct sequences representing 10 different classes have been identified. On the other hand, cDNAs for only three Gβ-subunit genes have been isolated so far. All three of the Gβ genes have been chromosomally mapped in the human, but only two in the mouse. Using a human retinal cDNA for the third G protein β-subunit, we have mapped the corresponding gene, termed Gnb-3, to mouse Chromosome 6 with somatic cell hybrids and have positioned it distal to but near the marker Raf-1 by analysis of the progeny of three genetic crosses.     

Molecular organisation of the malate synthase genes of Aspergillus nidulans and Neurospora crassa

Summary A soybean nodulin cDNA clone (E41) hybrid-selected mRNA for three in vitro translation products with apparent molecular weights of 26 kDa, 25 kDa and 24 kDa. Based on Southern analysis of soybean genomic DNA, combined with mapping and sequencing of genomic clones, we identified four genes that are related to E41, one of which was identified to be the previously characterized N-20 gene. Our data indicate the linkage of three of the genes, of which one is a truncated version and suggest that they originated by gene duplication combined with deletion and conversion. The genes are highly expressed and we postulate that the sequence conservation in the 5 and 3 flanking regions of all four genes, has a functional role in their expression. Hybrid-selected translation products of E41 are not immunoprecipitable with antibody to the soluble fraction of nodules suggesting that they are membrane associated. The N-20 gene, which is a member of this gene subfamily, showed sequence similarity to four previously characterized nodulin genes and a phylogenetic tree is proposed based on the extent of sequence similarity.     

The pentafunctional FAS1 genes of Saccharomyces cerevisiae and Yarrowia lipolytica are co-linear and considerably longer than previously estimated

Summary The fatty acid synthetase (FAS) gene FAS1 of the alkane-utilizing yeast Yarrowia lipolytica was cloned and sequenced. The gene is represented by an intron-free reading frame of 6228 by encoding a protein of 2076 amino acids and 229980 Da molecular weight. This protein exhibits a 58% sequence similarity to the corresponding Saccharomyces cerevisiae FAS -subunit. The sequential order of the five FAS1-encoded enzyme domains, acetyl transferase, enoyl reductase, dehydratase and malonyl/palmityl-transferase, is co-linear in both organisms. This finding agrees with available evidence that the functional organization of FAS genes is similar in related organisms but differs considerably between unrelated species. In addition, previously reported conflicting data concerning the 3 end of S. cerevisiae FAS1 were re-examined by genomic and cDNA sequencing of the relevant portion of the gene. Thereby, the translational stop codon was shown to lie considerably downstream of both published termination sites. The S. cerevisiae FAS1 gene thus has a corrected length of 6153 by and encodes a protein of 2051 amino acids and 228667 Da molecular weight.