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1.
Population genetics and phylogenetics of DNA sequence variation at multiple loci within the Drosophila melanogaster species complex 总被引:14,自引:1,他引:13
Two regions of the genome, a 1-kbp portion of the zeste locus and a 1.1-
kbp portion of the yolk protein 2 locus, were sequenced in six individuals
from each of four species: Drosophila melanogaster, D. simulans, D.
mauritiana, and D. sechellia. The species and strains were the same as
those of a previous study of a 1.9-kbp region of the period locus. No
evidence was found for recent balancing or directional selection or for the
accumulation of selected differences between species. Yolk protein 2 has a
high level of amino acid replacement variation and a low level of
synonymous variation, while zeste has the opposite pattern. This contrast
is consistent with information on gene function and patterns of codon bias.
Polymorphism levels are consistent with a ranking of effective population
sizes, from low to high, in the following order: D. sechellia, D.
melanogaster, D.mauritiana, and D. simulans. The apparent species
relationships are very similar to those suggested by the period locus
study. In particular, D. simulans appears to be a large population that is
still segregating variation that arose before the separation of D.
mauritiana and D. sechellia. It is estimated that the separation of
ancestral D. melanogaster from the other species occurred 2.5-3.4 Mya. The
separations of D. sechellia and D. mauritiana from ancestral D. simulans
appear to have occurred 0.58- 0.86 Mya, with D. mauritiana having diverged
from ancestral D. simulans 0.1 Myr more recently than D. sechellia.
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Conjugal transfer of three IncP1 plasmids and one IncFII plasmid into strains of the ethanol-producing bacterium Zymomonas mobilis was obtained. These plasmids were transferred at high frequencies from Escherichia coli and Pseudomonas aeruginosa into Z. mobilis and also between different Z. mobilis strains, using the membrane filter mating technique. Most of the plasmids were stably maintained in Z. mobilis, although there was some evidence of delayed marker expression. A low level of chromosomal gene transfer, mediated by plasmid R68.45, was detected between Z. mobilis strains. Genetic evidence suggesting that Z. mobilis may be more closely related to E. coli than to Pseudomonas or Rhizobium is discussed. 相似文献
4.
Constitutive and repressivle enzymes of the common pathway of aromatic biosynthesis in Escherichia coli K-12: regulation of enzyme synthesis at different growth rates. 总被引:3,自引:0,他引:3 下载免费PDF全文
Synthesis of five of the enzymes of the common pathway of aromatic biosynthesis has been shown to be unaffected by either the aromatic amino acids--the product of the first reaction (3-deoxy-D-arabinoheptulosonic acid-7-phosphate) or the product of the last reaction (chorismate)--or by the state of regulator gene loci tyrR. On the other hand, the rate of synthesis of these enzymes, and of several other enzymes for which repression control was inactive because of mutations in relevant regulator genes, was found to change with growth rate. These changes were found to correlate at faster growth rates than those observed in glucose minimal medium with the alterations in the relative frequencies of the corresponding structural genes which occur at these growth rates. It was found that when wild-type cells were grown at these faster growth rates in medium lacking the aromatic amino acids, complete derepression of the tyrosine-inhibitable 3-deoxy-D-arabinoheptulosonic acid-7-phosphate synthetase occurred, in strong contrast to the situation when wild-type cells are grown in glucose minimal medium. 相似文献
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Summary Cell recycle studies have been carried out with a strain of Zymomonas mobilis selected for its improved ethanol tolerance and faster rates of glucose uptake and ethanol production. As part of the investigation a capilliary cross-flow microfiltration unit with polyamide membranes has been evaluated in view of its potential advantages (low cost and ability to withstand repeated cleaning with caustic soda). The results demonstrate that ethanol concentrations of 60–65g/l can be sustained at productivities ranging from 120–200g/l/h. 相似文献
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C García-Vielma MI Dávila-Rodríguez F Hernández-Garza RM Cerda-Flores 《Biotechnic & histochemistry》2016,91(2):102-107
We performed a hospital-based, unmatched case-control study to investigate the association between progressive stages of cervical neoplasia and digital analysis of cell proliferation by silver stained nucleolus organizer region associated proteins (AgNORs). We measured cell proliferation levels in the cervical epithelial cells of 10 women with low grade squamous intraepithelial lesions (LG-SIL), eight with high grade squamous intraepithelial lesions (HG-SIL), 11 with cervical cancer (CC) and eight with no cervical lesions (controls) using the AgNORs technique. Cell proliferation was measured by digital image analysis (DIA). DIA revealed increased total areas of AgNORs in HG-SIL and CC compared to LG-SIL and control patients. AgNORs with a kidney or cluster shape exhibited greater areas than those with a spherical or long shape. We propose a cut-off of 118 pixels to differentiate benign (control and LG-SIL) from malignant (HG-SIL and CC) lesions. DIA of AgNORs is a simple and inexpensive method for studying proliferation. The increased total area of AgNORs in malignant lesions provides information regarding cell behavior and may be related to cervical carcinogenesis; however, further validation studies are required to establish its usefulness in cytological analysis. 相似文献
10.
1-Thio-beta-D-galactofuranosides: synthesis and evaluation as beta-D- galactofuranosidase inhibitors
Marino C; Marino K; Miletti L; Manso Alves MJ; Colli W; de Lederkremer RM 《Glycobiology》1998,8(9):901-904
Beta-D-galactofuranosidase is a good chemotherapeutic target for the design
of inhibitors, since beta-D-galactofuranose is a constituent of important
parasite glycoconjugates but is not present in the host mammals. With this
aim, we have synthesized for the first time alkyl, benzyl and aryl
1-thio-beta-D-galactofuranosides by condensation of
penta-O-benzoyl-alpha,beta-D-galactofuranose with the corresponding thiols,
in the presence of SnCl4as catalyst. The complete chemical and
spectroscopical characterization of these compounds showed that the
reaction was stereoselective. Debenzoylation with sodium methoxide afforded
the beta-S-galactofuranosides in high yield. The thioglycosides were tested
as inhibitors of the beta-D- galactofuranosidase of Penicillium fellutanum,
using for the first time 4-nitrophenyl-beta-D-galactofuranoside as
chromogenic substrate. The 4- aminophenyl-1-thio-beta-D-galactofuranoside,
obtained by catalytic hydrogenation of the nitrophenyl derivative, was the
best inhibitor being then an adequate ligand for the preparation of an
affinity phase aimed at the isolation of beta-d-galactofuranosidases from
different sources. Also the inhibitory activity of d-galactono-1, 4-lactone
was shown.
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