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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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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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5.
Mapping of susceptibility to Marek's disease within the major histocompatibility (B) complex by refined typing of White Leghorn chickens 总被引:2,自引:0,他引:2
B. G. Hepkema E. J. Hensen J. J. Blankert A. J.van der Zijpp G. A. A. Albers M. G. J. Tilanus E. Egberts 《Animal genetics》1993,24(4):283-287
The major histocompatibility (B) complex of a distinct commercial pure White Leghorn chicken line was characterized using serological, biochemical and restriction fragment length polymorphism (RFLP) typing. Line B chickens displayed a high recombination frequency within the B complex. Three recombinant haplo-types were identified. The influence of these haplotypes was determined in relation to the haplotypes Bl9 and B21 on their resistance to Marek's disease (MD) in an experimental infection with the virus. Offspring of sires with a recombinant haplotype in combination with B19 or B21, and dams, which were homozygous B19/B19 or B21/B21 were infected. The B type of the offspring had a significant effect upon survival. Animals with B complex types B21/B21, B134/B21 and B234/B21 were relatively resistant to MD (24–32% mortality), whereas B19/B19 birds were highly susceptible (68% mortality). Animals with a recombinant halpotype B19r21 (B-G21, B-F19) were equally susceptible to MD as birds with the complete B19 haplotype. In contrast to earlier publications, resistance was not inherited as a dominant trait. Apparently, B19 was associated with a dominant susceptibility. The gene(s) associated with the B complex and involved in resistance to MD were localized within the B-F/B-L region. However, the association with a presumably non-coding subregion of B-G could not be excluded. 相似文献
6.
Marcel Janse Bert-Jan F. de Rooij Bart van Hoek Arie P. van den Berg Robert J. Porte Hans Blokzijl Minneke J. Coenraad Bouke G. Hepkema Alexander F. Schaapherder Jan Ringers Rinse K. Weersma Hein W. Verspaget 《PloS one》2013,8(8)
Introduction
Orthotopic liver transplantation (OLT) is accompanied by a significant postoperative infection risk. Immunosuppression to prevent rejection increases the susceptibility to infections, mainly by impairing the adaptive immune system. Genetic polymorphisms in the lectin complement pathway of the donor have recently been identified as important risk determinants of clinically significant bacterial infection (CSI) after OLT. Another genetic factor involved in innate immunity is NOD2, which was reported to be associated with increased risk of spontaneous bacterial peritonitis in cirrhotic patients.Methods
We assessed association of three genetic NOD2 variants (R702W, G908R and 3020insC) with increased risk of CSI after OLT. 288 OLT recipient-donor pairs from two tertiary referral centers were genotyped for the three NOD2 variants. The probability of CSI in relation to NOD2 gene variants was determined with cumulative incidence curves and log-rank analysis.Results
The R702W NOD2 variant in the recipient was associated with CSI after OLT. Eight out of 15 (53.3%) individuals with a mutated genotype compared to 80/273 (29.3%) with wild type genotype developed CSI (p=0.027, univariate cox regression), illustrated by a higher frequency of CSI after OLT over time (p=0.0003, log rank analysis). Multivariate analysis (including the donor lectin complement pathway profile) showed independence of this R702W NOD2 association from other risk factors (HR 2.0; p=0.04). The other NOD2 variants, G908R and 3020insC, in the recipient were not associated with CSI. There was no association with CSI after OLT for any of the NOD2 variants in the donor.Conclusion
The mutated NOD2 R702W genotype in the recipient is independently associated with an increased risk of bacterial infections after liver transplantation, indicating a predisposing role for this genetic factor impairing the recipient’s innate immune system. 相似文献7.
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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8.
Mark C. Dessing Jesper Kers Jeffrey Damman Henri G. D. Leuvenink Harry van Goor Jan-Luuk Hillebrands Bouke G. Hepkema Harold Snieder Jacob van den Born Martin H. de Borst Stephan J. L. Bakker Gerjan J. Navis Rutger J. Ploeg Sandrine Florquin Marc Seelen Jaklien C. Leemans 《PloS one》2015,10(10)
Toll-like receptors (TLRs) play a crucial role in innate- and adaptive immunity. The TLR pathways were shown to play key functional roles in experimental acute and chronic kidney injury, including the allo-immune response after experimental renal transplantation. Data about the precise impact of TLRs and their negative regulators on human renal transplant outcomes however are limited and contradictory. We studied twelve non-synonymous single nucleotide polymorphisms (SNPs) of which eleven in TLR1-8 and one in SIGIRR in a final cohort comprising 1116 matching donors and recipients. TLR3 p.Leu412Phe and SIGIRR p.Gln312Arg significantly deviated from Hardy-Weinberg equilibrium and were excluded. The frequency distribution of the minor alleles of the remaining 10 TLR variants were compared between patients with end-stage renal disease (recipients) and controls (kidney donors) in a case-control study. Secondly, the associations between the minor allele frequency of the TLR variants and delayed graft function, biopsy-proven acute rejection and death-censored graft failure after transplantation were investigated with Cox regression. Carrier frequencies of the minor alleles of TLR1 p.His305Leu (OR = 4.79, 95% CI = 2.35–9.75, P = 0.0002), TLR1 p.Asn248Ser (OR = 1.26, 95% CI = 1.07–1.47, P = 0.04) and TLR8 p.Met1Val (OR = 1.37, 95% CI = 1.14–1.64, P = 0.008) were significantly higher in patients with ESRD, with little specificity for the underlying renal disease entity (adjusted for age, gender and donor-recipient relatedness). The minor allele frequency of none of the TLR variants significantly associated with the surrogate and definite outcomes, even when multivariable models were created that could account for TLR gene redundancy. In conclusion, genetic variants in TLR genes were associated with the prevalence of ESRD but not renal transplant outcomes. Therefore, our data suggests that specific TLR signaling routes might play a role in the final common pathway of primary renal injury. A role for TLR signaling in the context of renal transplantation is probably limited. 相似文献
9.
Huang X Hepkema B Nolte I Kushekhar K Jongsma T Veenstra R Poppema S Gao Z Visser L Diepstra A van den Berg A 《PloS one》2012,7(2):e31865
HLA-A2 protects from EBV+ classical Hodgkin lymphoma (cHL) in Western Europe, but it is unknown whether this protective effect also exists in the Chinese population. We investigated the association of HLA-A2 and specific common and well documented HLA-A2 subtypes with EBV stratified cHL patients (n = 161) from the northern part of China. Quantitative-PCR and sequence-based subtyping was performed to identify HLA-A2 positive samples and their subtypes. 67 (42%) of the cHL patients were EBV+. There were no significant differences in percentages of HLA-A2 positivity between cHL and controls (65% vs 66%) and between EBV+ and EBV− cHL patients (70% vs 61%). The frequency distribution of HLA-A2 subtypes was significantly different between EBV stratified cHL subgroups and controls. This difference was most striking for the HLA-A*02:07 type with a frequency of 38% in EBV+ cHL, 8% in EBV− cHL and 20% in controls. Significant differences were also observed for the HLA-A*02:07, HLA-A2 (non-02:07) and the A2-negative typings between EBV+ cHL vs controls (p = 0.028), EBV− cHL vs controls (p = 0.045) and EBV+ vs EBV− cHL cases (p = 2×10−5). In conclusion, HLA-A*02:07 is a predisposing allele for EBV+ cHL and a protective allele for EBV− cHL in the northern Chinese population. 相似文献
10.
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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