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1.
Transcriptional control, translation and function of the products of the five open reading frames of the Escherichia coli nir operon 总被引:3,自引:0,他引:3
Nerina R. Harborne Lesley Griffiths Stephen J. W. Busby Jeffrey A. Cole 《Molecular microbiology》1992,6(19):2805-2813
Five open reading frames designated nirB, nirD, nirE, nirC and cysG have been identified from the DNA sequence of the Escherichia coli nir operon. Complementation experiments established that the NirB, NirD and CysG polypeptides are essential and sufficient for NADH-dependent nitrite reductase activity (EC 1.6.6.4). A series of plasmids has been constructed in which each of the open reading frames has been fused in-phase with the beta-galactosidase gene, lacZ. Rates of beta-galactosidase synthesis during growth in different media revealed that nirB, -D, -E and -C are transcribed from the FNR-dependent promoter, p-nirB, located just upstream of the nirB gene: expression is co-ordinately repressed by oxygen and induced during anaerobic growth. Although the nirB, -D and -C open reading frames are translated into protein, no translation of nirE mRNA was detected. The cysG gene product is expressed from both p-nirB and a second, FNR-independent promoter, p-cysG, located within the nirC gene. No NADH-dependent nitrite reductase activity was detected in extracts from bacteria lacking either NirB or NirD, but a mixture of the two was as active as an extract from wild-type bacteria. Reconstitution of enzyme activity in vitro required stoichiometric quantities of NirB and NirD and was rapid and independent of the temperature during mixing. NirD remained associated with NirB during the initial stages of purification of the active enzyme, suggesting that NirD is a second structural subunit of the enzyme. 相似文献
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Rachael V. Gallagher Lesley Hughes Michelle R. Leishman Peter D. Wilson 《Biological invasions》2010,12(12):4049-4063
Potential interactions between climate change and exotic plant invasions may affect areas of high conservation value, such
as land set aside for the protection of endangered species or ecological communities. We investigated this issue in eastern
Australia using species distribution models for five exotic vines under climate regimes for 2020 and 2050. We examined how
projected changes in the distribution of climatically suitable habitat may coincide with the remaining remnants of an endangered
ecological community—littoral rainforests—in this region. The number of known infestations of each weed in tropical, subtropical
and temperate areas was used to assess the likelihood of further expansion into areas projected to provide suitable habitat
under future conditions. Littoral rainforest reserves were consistently predicted to provide bioclimatically suitable habitat
for the five vines examined under both current and future climate scenarios. We explore the consequences and potential strategies
for managing exotic plant invasions in these protected areas in the coming decades. 相似文献
4.
Influence of paternally imprinted genes on development. 总被引:4,自引:0,他引:4
S C Barton A C Ferguson-Smith R Fundele M A Surani 《Development (Cambridge, England)》1991,113(2):679-687
The parental origin of chromosomes is critical for normal development in the mouse because some genes are imprinted resulting in a predetermined preferential expression of one of the alleles. Duplication of the paternal (AG: androgenones) or maternal (GG/PG: gynogenones/parthenogenones) genomes will result in an excess or deficiency of gene dosage with corresponding phenotypic effects. Here, we report on the effects of paternally imprinted genes on development following introduction of the AG inner cell mass into normal blastocysts. There was a striking increase in embryonic growth by up to 50%, and a characteristic change in embryonic shape, partly because of the corresponding increase in length of the anterior-posterior axis. These changes, between e12-e15, were proportional to the contribution from AG cells to the embryo. However, a contribution of AG cells in excess of 50% was invariably lethal as development progressed to e15. A limited number of chimeras were capable of full-term development provided there was a relatively low contribution from AG cells. The distribution of AG cells in chimeras was not uniform, especially later in development when there was a disproportionate presence of AG cells in the mesodermally derived tissues. Their contribution was consistently greater in the heart and skeletal muscle, but was considerably lower in the brain. Chimeras detected after birth were either dead or developed severe abnormalities of the skeletal elements, particularly of the ribs which were enlarged, distorted and fused, with greatly increased cartilaginous material with an absence of normal ossification. These phenotypic effects in chimeras are reciprocal to those observed in the presence of GG/PG cells, which resulted in a substantial size reduction approaching 50%.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
5.
Caroline van Haaften-Day Peter Russell Susan Carr Lesley Wright 《In vitro cellular & developmental biology. Plant》1988,24(10):965-971
Summary A cell line derived from a human ovarian carcinosarcoma was established in tissue culture and in nude mice. Two sublines,
LDF and HDF, separated by discontinuous density centrifugation were also established from the parent line JoN. The cloning
efficiency of the JoN line was 21%. Morphologic features of adenocarcinoma cells characteristic of the parent JoN cells were
retained in the sublines and clones; all lines showed the same karyotype and DNA content (pseudodiploid and pseudotetraploid).
Keratin, as demonstrated immunohistochemically, was strongly expressed in the parent line JoN and the xenograft tumor, but
not at all in the LDF sublines and only moderately in the HDF sublines. Vimentin, however, was expressed in neither the parent
line JoN nor the xenograft tumor, but was present in both sublines. Transglutaminase and plasminogen activator activity was
high in the parent line JoN. Neither, sublines nor clones showed the same high enzyme activity as the parent line. It is concluded
that this human tumor line JoN is comprised of epithelial cells, capable of multidirectional differentiation. 相似文献
6.
The binding of 3H-corticosterone and 3H-11-dehydrocorticosterone to receptors in cytosol and nucleus was examined in fetal mouse brain and placenta using Sephadex gel filtration or charcoal to separate bound and unbound steroid. In the cytosol, competitive displacement of each steroid by the other was observed. The binding was unaffected by RNase, DNase, dithiothreitol or N-ethyl maleimide but was diminished by Pronase. Nuclei were isolated by hypotonic shock using dilute MgCl2 and the steroid receptor-complexes of both steroids were obtained from the nuclear sap. Receptor-complexes of both steroids were observed in brain and placental tissues. Competitive displacement of each steroid by the other was also observed in nuclear binding. Both 11-dehydrocorticosterone and 11-deoxycorticosterone bound to a chromatin fraction as did the hormone corticosterone. Identity of the steroids was established by using chromatography and co-crystallization techniques. This work raises the possibility that in the fetal mouse, 11-dehydrocorticosterone, previously considered biologically inactive and an abundant metabolite in fetal mouse tissues, may in fact play a more positive role in regulation. 相似文献
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8.
Michaelis-Menten kinetics for exoglucanase, endoglucanase and β-glucosidase activities from two different strains of Aspergillus fumigatus were compared in the absence and the presence of ammonium ions. Inhibitory effects, evident in only one strain, were quantified, suggesting non-competitive inhibition for endoglucanase and β-glucosidase, but competitive inhibition of exocellulase. Possible reasons are discussed. 相似文献
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