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1.
Maintenance of the cellobiose utilization genes of Escherichia coli in a cryptic state 总被引:6,自引:1,他引:5
The genes for cellobiose utilization are normally cryptic in Escherichia
coli. The cellobiose system was used as a model to understand the process
by which silent genes are maintained in microbial populations. Previously
reported was (1) the isolation of a mutant strain that expresses the
cellobiose-utilization (Cel) genes and (2) that expression of those genes
allows utilization of three beta- glucoside sugars: cellobiose, arbutin,
and salicin. The Cel gene cluster has now been cloned from that mutant
strain. In the course of locating the Cel genes within the cloned DNA
segment, it was discovered that inactivation of the Cel-encoded hydrolase
rendered the host strain sensitive to all three beta-glucosides as potent
inhibitors. This sensitivity arises from the accumulation of the
phosphorylated beta- glucosides. Because even the fully active genes
conferred some degree of beta-glucoside sensitivity, the effects of
cellobiose on a series of five Cel+ mutants of independent origin were
investigated. Although each of those strains utilizes cellobiose as a sole
carbon and energy source, cellobiose also acts as a potent inhibitor that
reduces the growth rate on glycerol 2.5-16.5-fold. On the other hand,
wild-type strains that cannot utilize cellobiose are not inhibited. The
observation that the same compound can serve either as a nutrient or as an
inhibitor suggests that, under most conditions in which cellobiose will be
present together with other resources, there is a strong selective
advantage to having the cryptic (Cel0) allele. In those environments in
which cellobiose is the sole, or the best, resource, mutants that express
the genes (Cel+) will have a strong selective advantage. It is suggested
that temporal alternation between these two conditions is a major factor in
the maintenance of these genes in E. coli populations. This alternation of
environments and fitnesses was predicted by the model for cryptic-gene
maintenance that was previously published.
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2.
Selection-induced mutations are nonrandom mutations that occur as specific
and direct responses to environmental challenge. Examples of
selection-induced mutations have been reported both in bacteria and in
yeast. I previously showed (Hall 1988) that excisions of the mobile genetic
element IS150 from within bglF are selection induced and argued that they
occurred because they were potentially advantageous under the selective
conditions employed. Mittler and Lenski (Mittler and Lenski 1992) have
argued that such excisions are not selection induced but that they occur
randomly in nondividing cells. Here I provide further evidence that IS150
excisions are induced by selection and that the excisions are immediately,
rather than only potentially, advantageous to the cell. I also provide
evidence that excisions, which Mittler and Lenski claim occur randomly in
saturated broth cultures, actually occur after samples from those cultures
are plated onto selective medium.
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3.
Reactive oxygen species generation is independent of de novo sphingolipids in apoptotic photosensitized cells 总被引:2,自引:0,他引:2
Our recent studies have shown that the de novo sphingolipids play a role in apoptosis of photosensitized cells. To elucidate the involvement of the de novo sphingolipids in reactive oxygen species (ROS) production and mitochondrial depolarization during apoptosis, the stress inducer photodynamic therapy (PDT) with the photosensitizer Pc 4 was used. In Jurkat cells PDT-triggered ROS production or mitochondrial membrane potential (deltapsi(m)) loss was not prevented by the de novo sphingolipid synthesis inhibitor ISP-1. However, PDT + C16-ceramide led to enhanced mitochondrial depolarization and DEVDase activation. The superoxide dismutase mimic manganese (III) tetrakis (4-benzoic acid) porphyrin (MnTBAP) protected Jurkat cells from ROS generation and apoptosis, but not from deltapsi(m) reduction. Sphinganine or C16-ceramide counteracted MnTBAP-induced protection from apoptosis in Jurkat, as well as CHO cells. In LY-B cells, CHO-derived mutants deficient in serine palmitoyltransferase (SPT) activity and the de novo sphingolipid synthesis, mitochondrial depolarization, but not ROS generation, was suppressed post-PDT. In LY-B cells transfected with the SPT component LCB1, deltapsi(m) collapse post-PDT was restored. The data support the following hypotheses: MnTBAP protects against apoptosis via steps downstream of deltapsi(m) loss; de novo sphingolipids are not required for ROS generation, but can play a role in deltapsi(m) dissipation in photosensitized apoptotic cells. 相似文献
4.
Regulation of indoleamine 2,3-dioxygenase expression in simian immunodeficiency virus-infected monkey brains 总被引:2,自引:0,他引:2
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Burudi EM Marcondes MC Watry DD Zandonatti M Taffe MA Fox HS 《Journal of virology》2002,76(23):12233-12241
The human immunodeficiency virus type 1-associated cognitive-motor disorder, including the AIDS dementia complex, is characterized by brain functional abnormalities that are associated with injury initiated by viral infection of the brain. Indoleamine 2,3-dioxygenase (IDO), the first and rate-limiting enzyme in tryptophan catabolism in extrahepatic tissues, can lead to neurotoxicity through the generation of quinolinic acid and immunosuppression and can alter brain chemistry via depletion of tryptophan. Using the simian immunodeficiency virus (SIV)-infected rhesus macaque model of AIDS, we demonstrate that cells of the macrophage lineage are the main source for expression of IDO in the SIV-infected monkey brain. Animals with SIV encephalitis have the highest levels of IDO mRNA, and the level of IDO correlates with gamma interferon (IFN-gamma) and viral load levels. In vitro studies on mouse microglia reveal that IFN-gamma is the primary inducer of IDO expression. These findings demonstrate the link between IDO expression, IFN-gamma levels, and brain pathology signs observed in neuro-AIDS. 相似文献
5.
High-level expression of the Endo-beta-N-acetylglucosaminidase F2 gene in E.coli: one step purification to homogeneity 总被引:1,自引:0,他引:1
The Endo F2gene was overexpressed in E.coli as a fusion protein joined to
the maltose-binding protein. MBP-Endo F2was found in a highly enriched
state as insoluble, inactive inclusion bodies. Extraction of the inclusion
bodies with 20% acetic acid followed by exhaustive dialysis rendered the
fusion protein active and soluble. MBP-Endo F2was digested with Factor
Xaand purified on Q-Sepharose. The enzyme was homogeneous by SDS-PAGE, and
appeared as a single symmetrical peak on HPLC. Analysis of the
amino-terminus demonstrated conclusively that recombinant Endo F2was
homogeneous and identical to the native enzyme.
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6.
Persistent nuclear ribosomal DNA sequence polymorphism in the Amelanchier agamic complex (Rosaceae) 总被引:5,自引:0,他引:5
Campbell CS; Wojciechowski MF; Baldwin BG; Alice LA; Donoghue MJ 《Molecular biology and evolution》1997,14(1):81-90
Individual plants of several Amelanchier taxa contain many polymorphic
nucleotide sites in the internal transcribed spacers (ITS) of nuclear
ribosomal DNA (nrDNA). This polymorphism is unusual because it is not
recent in origin and thus has resisted homogenization by concerted
evolution. Amelanchier ITS sequence polymorphism is hypothesized to be the
result of gene flow between two major North American clades resolved by
phylogenetic analysis of ITS sequences. Western North American species plus
A. humilis and A. sanguinea of eastern North America form one clade (A),
and the remaining eastern North American Amelanchier make up clade B. Five
eastern North American taxa are polymorphic at many of the nucleotide sites
where clades A and B have diverged and are thought to be of hybrid origin,
with A. humilis or A. sanguinea as one parent and various members of clade
B as the other parent. Morphological evidence suggests that A. humilis is
one of the parents of one of the polymorphic taxa, a microspecies that we
refer to informally as A. "erecta." Sequences of 21 cloned copies of the
ITS1- 5.8S gene-ITS2 region from one A. "erecta" individual are identical
to A. humilis sequence or to the clade B consensus sequence, or they are
apparent recombinants of A. humilis and clade B ITS repeats. Amelanchier
"erecta" and another polymorphic taxon are suspected to be relatively old
because both grow several hundred kilometers beyond the range of one of
their parents. ITS sequence polymorphisms have apparently persisted in
these two taxa perhaps because of polyploidy and/or agamospermy (asexual
seed production), which are prevalent in the genus.
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7.
Elke M Lohmeier-Vogel David Kerk Mhairi Nimick Susan Wrobel Lori Vickerman Douglas G Muench Greg BG Moorhead 《BMC plant biology》2008,8(1):120
Background
Starch accumulation and degradation in chloroplasts is accomplished by a suite of over 30 enzymes. Recent work has emphasized the importance of multi-protein complexes amongst the metabolic enzymes, and the action of associated non-enzymatic regulatory proteins. Arabidopsis At5g39790 encodes a protein of unknown function whose sequence was previously demonstrated to contain a putative carbohydrate-binding domain. 相似文献8.
Lysine acetylome profiling uncovers novel histone deacetylase substrate proteins in Arabidopsis
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Paul J Boersema Jan‐Oliver Jost Katharina Kramer Ahmet Bakirbas Julia Sindlinger Magdalena Plöchinger Dario Leister Glen Uhrig Greg BG Moorhead Jürgen Cox Michael E Salvucci Dirk Schwarzer Matthias Mann Iris Finkemeier 《Molecular systems biology》2017,13(10)
Histone deacetylases have central functions in regulating stress defenses and development in plants. However, the knowledge about the deacetylase functions is largely limited to histones, although these enzymes were found in diverse subcellular compartments. In this study, we determined the proteome‐wide signatures of the RPD3/HDA1 class of histone deacetylases in Arabidopsis. Relative quantification of the changes in the lysine acetylation levels was determined on a proteome‐wide scale after treatment of Arabidopsis leaves with deacetylase inhibitors apicidin and trichostatin A. We identified 91 new acetylated candidate proteins other than histones, which are potential substrates of the RPD3/HDA1‐like histone deacetylases in Arabidopsis, of which at least 30 of these proteins function in nucleic acid binding. Furthermore, our analysis revealed that histone deacetylase 14 (HDA14) is the first organellar‐localized RPD3/HDA1 class protein found to reside in the chloroplasts and that the majority of its protein targets have functions in photosynthesis. Finally, the analysis of HDA14 loss‐of‐function mutants revealed that the activation state of RuBisCO is controlled by lysine acetylation of RuBisCO activase under low‐light conditions. 相似文献
9.
Fecapentaenes are a class of conjugated ether lipids which have been identified as the major component of human fecal mutagenicity in the Ames Salmonella mutagenesis assay. Human epidemiologic data have indicated that most healthy North American populations eating a western diet do excrete detectable levels of fecapentaenes. Excreted fecapentaene levels seem to reflect levels throughout the colonic lumen, and levels vary characteristically between individuals. Those individuals found to excrete high levels of fecapentaene appear, based on limited data, to be at decreased risk of colorectal neoplasia. Carcinogenicity studies in rats and mice have been predominantly negative, however, increased tumor incidence in mice exposed to fecapentaenes as neonates has recently been reported. Fecapentaenes are direct-acting genotoxins, which may react with DNA through free radical mechanisms, and/or aldehyde formation. Mechanisms by which fecapentaene-induced DNA damage may mediate carcinogenesis are discussed. 相似文献
10.
In four experiments, we examined the effects on the affiliative preferences of 'focal' female Japanese quail given the opportunity to watch a conspecific male interact with a 'model' female. Experiments were conducted in three, 10-min phases: (1) a pretest, during which a 'focal' female chose between two males; (2) an observation phase, when each focal female watched the male she had spent less time near during the pretest (her 'nonpreferred' male) interact with a 'model' quail; and (3) a post-test, during which each focal female again chose between her nonpreferred and preferred males. Focal females increased their preferences for nonpreferred males after seeing them together with a model female (but not a model male), even if the nonpreferred male and model female were separated by an opaque barrier that prevented them from interacting. A focal female's preference for the end of the enclosure containing her nonpreferred male was not increased when she either watched him court a concealed model female or watched a model female that was being courted by him. Taken together, the present results suggest that a simple tendency for females to approach areas where they have previously seen a male and female quail, in preference to locations where they have seen only a male quail, can explain some of the effect of watching a nonpreferred male mate on a female's tendency to affiliate with him. However, focal females also showed enhanced preferences for nonpreferred males they had seen mating after we both moved those males and controlled for effects of transposition. Thus, processes akin to both 'mate choice copying' and 'conspecific cueing' remain viable explanations for the increase in a focal female quail's tendency to affiliate with a male she watched mate with another female. Copyright 1999 The Association for the Study of Animal Behaviour. 相似文献