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81.
Dephosphorylation of cdc25-C by a type-2A protein phosphatase: specific regulation during the cell cycle in Xenopus egg extracts. 总被引:16,自引:5,他引:11
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We have examined the roles of type-1 (PP-1) and type-2A (PP-2A) protein-serine/threonine phosphatases in the mechanism of activation of p34cdc2/cyclin B protein kinase in Xenopus egg extracts. p34cdc2/cyclin B is prematurely activated in the extracts by inhibition of PP-2A by okadaic acid but not by specific inhibition of PP-1 by inhibitor-2. Activation of the kinase can be blocked by addition of the purified catalytic subunit of PP-2A at a twofold excess over the activity in the extract. The catalytic subunit of PP-1 can also block kinase activation, but very high levels of activity are required. Activation of p34cdc2/cyclin B protein kinase requires dephosphorylation of p34cdc2 on Tyr15. This reaction is catalysed by cdc25-C phosphatase that is itself activated by phosphorylation. We show that, in interphase extracts, inhibition of PP-2A by okadaic acid completely blocks cdc25-C dephosphorylation, whereas inhibition of PP-1 by specific inhibitors has no effect. This indicates that a type-2A protein phosphatase negatively regulates p34cdc2/cyclin B protein kinase activation primarily by maintaining cdc25-C phosphatase in a dephosphorylated, low activity state. In extracts containing active p34cdc2/cyclin B protein kinase, dephosphorylation of cdc25-C is inhibited, whereas the activity of PP-2A (and PP-1) towards other substrates is unaffected. We propose that this specific inhibition of cdc25-C dephosphorylation is part of a positive feedback loop that also involves direct phosphorylation and activation of cdc25-C by p34cdc2/cyclin B. Dephosphorylation of cdc25-C is also inhibited when cyclin A-dependent protein kinase is active, and this may explain the potentiation of p34cdc2/cyclin B protein kinase activation by cyclin A. In extracts supplemented with nuclei, the block on p34cdc2/cyclin B activation by unreplicated DNA is abolished when PP-2A is inhibited or when stably phosphorylated cdc25-C is added, but not when PP-1 is specifically inhibited. This suggests that unreplicated DNA inhibits p34cdc2/cyclin B activation by maintaining cdc25-C in a low activity, dephosphorylated state, probably by keeping the activity of a type-2A protein phosphatase towards cdc25-C at a high level. 相似文献
82.
Kerstin Schüddekopf Silke Hennecke Ute Liese Michael Kutsche Werner Klipp 《Molecular microbiology》1993,8(4):673-684
To identify Rhodobacter capsulatus nif genes necessary for the alternative nitrogenase, strains carrying defined mutations in 32 genes and open reading frames of nif region A, B or C were constructed. The ability of these mutants to grow on nitrogen-free medium with molybdenum (Nif phenotype) or in a nifHDK deletion background on medium without molybdenum (Anf phenotype) was tested. Nine nif genes and nif-associated coding regions are absolutely essential for the alternative nitrogenase. These genes comprise nifV and nifB, the nif-specific ntr system (nifR1, R2, R4) and four open reading frames, which exhibit no homology to known genes. In addition, a significantly reduced activity of both the alternative nitrogenase and the molybdenum-dependent nitrogenase was found for fdxN mutants. By random Tn5 mutagenesis of a nifHDK deletion strain 42 Anf? mutants were isolated. Southern hybridization experiments demonstrated that 17 of these Tn5 mutants were localized in at least 13 different restriction fragments outside of known nif regions. Ten different Anf? Tn5 mutations are clustered on a 6 kb DNA fragment of the chromosome designated anf region A. DNA sequence analysis revealed that this region contained the structural genes of the alternative nitrogenase (anfHDGK). The identification of several Tn5 insertions mapping outside of anf region A indicated that at least 10 genes specific for the alternative nitrogenase are present in R. capsulatus. 相似文献
83.
Sven Rossel Patricia Kaiser Maya Bode-Dalby Jasmin Renz Silke Laakmann Holger Auel Wilhelm Hagen Pedro Martínez Arbizu Janna Peters 《Molecular ecology resources》2023,23(2):382-395
Species identification is pivotal in biodiversity assessments and proteomic fingerprinting by MALDI-TOF mass spectrometry has already been shown to reliably identify calanoid copepods to species level. However, MALDI-TOF data may contain more information beyond mere species identification. In this study, we investigated different ontogenetic stages (copepodids C1–C6 females) of three co-occurring Calanus species from the Arctic Fram Strait, which cannot be identified to species level based on morphological characters alone. Differentiation of the three species based on mass spectrometry data was without any error. In addition, a clear stage-specific signal was detected in all species, supported by clustering approaches as well as machine learning using Random Forest. More complex mass spectra in later ontogenetic stages as well as relative intensities of certain mass peaks were found as the main drivers of stage distinction in these species. Through a dilution series, we were able to show that this did not result from the higher amount of biomass that was used in tissue processing of the larger stages. Finally, the data were tested in a simulation for application in a real biodiversity assessment by using Random Forest for stage classification of specimens absent from the training data. This resulted in a successful stage-identification rate of almost 90%, making proteomic fingerprinting a promising tool to investigate polewards shifts of Atlantic Calanus species and, in general, to assess stage compositions in biodiversity assessments of Calanoida, which can be notoriously difficult using conventional identification methods. 相似文献
84.
J Hoffmann C Westendorff D Troitzsch U Ernemann S Reinert 《Biomedizinische Technik》2004,49(7-8):199-201
Laser-induced interstitial thermal therapy (LITT) is a proven minimally invasive surgical technique for the treatment of haemangiomas and vascular malformations, and various tumours. The intra-lesion application of thermal energy destroys regional tissue. The percutaneous placement of the laser fibre for photocoagulation is done without the benefit of direct visual control. Image-data-based LITT was performed in patients (five procedures) with extensive venous malformations in the maxillofacial area. The system comprised a specially developed Nd:YAG laser fibre introducer set used in conjunction with fused high-resolution computed tomography, and magnetic resonance image-data--based surgical navigation. In all cases, follow-up examination clearly showed a diminishment in tumour volume, and all patients reported significant subjective improvement. The results suggest that navigation-guided LITT can be performed safely, preserving vital structures from collateral thermal damage. 相似文献
85.
Kristina Kusche Anne Hembach Silke Hagner-Holler Wolfgang Gebauer Thorsten Burmester 《European journal of biochemistry》2003,270(13):2860-2868
Hemocyanins are large oligomeric copper-containing proteins that serve for the transport of oxygen in many arthropod species. While studied in detail in the Chelicerata and Crustacea, hemocyanins had long been considered unnecessary in the Myriapoda. Here we report the complete molecular structure of the hemocyanin from the common house centipede Scutigera coleoptrata (Myriapoda: Chilopoda), as deduced from 2D-gel electrophoresis, MALDI-TOF mass spectrometry, protein and cDNA sequencing, and homology modeling. This is the first myriapod hemocyanin to be fully sequenced, and allows the investigation of hemocyanin structure-function relationship and evolution. S. coleoptrata hemocyanin is a 6 x 6-mer composed of four distinct subunit types that occur in an approximate 2 : 2 : 1 : 1 ratio and are 49.5-55.5% identical. The cDNA of a fifth, highly diverged, putative hemocyanin was identified that is not included in the native 6 x 6-mer hemocyanin. Phylogenetic analyses show that myriapod hemocyanins are monophyletic, but at least three distinct subunit types evolved before the separation of the Chilopoda and Diplopoda more than 420 million years ago. In contrast to the situation in the Crustacea and Chelicerata, the substitution rates among the myriapod hemocyanin subunits are highly variable. Phylogenetic analyses do not support a common clade of Myriapoda and Hexapoda, whereas there is evidence in favor of monophyletic Mandibulata. 相似文献
86.
Alicia J. Hoffmann 《Journal of phycology》1988,24(2):203-208
Excised ligulae of Glossophora kunthii (C. Ag.) J. Ag. were cultured in photoperiods of 4–24 h and photon fluence rates of 10–75 μmol.m?2.s?1. Daylength interacted with irradiance on the growth of the ligulae. Maximal growth of primary ligulae occurred in long-day regimens with high irradiances suggesting an effect of irradiance on photosynthesis and growth. In contrast, growth of secondary ligulae was greatest in short-day regimes. Differences were significant at the highest irradiance tested. Differentiation of tetrasporangia on the ligulae is a short-day photoperiodic response. Daylengths of 8.5 h or less induced a sharp increase in numbers of fertile ligulae and tetrasporangia attaining maturity. Interruptions of the dark period decreased the development of tetrasporangia; the number of interruptions had a cumulative inhibitory effect. Differentiation of reproductive structures was influenced by interactions of photoperiod and irradiance. Maximum numbers of tetrasporangia were formed at short-day regimes and low irradiances; differentiation was completely inhibited at long-day conditions and high irradiance. 相似文献
87.
The soil algal communities of forested and reforested, limed and unlimed plots were compared in the acid rain impacted Kru sné hory Mountains. The floristic composition of unlimed plots is similar to that found in acid forest soils with a naturally low pH and no effect of the acid rain on these communities can be detected. Chlorophyceae are the only group present in these soils. In limed areas with a higher soil pH, algal diversity is significantly increased while algal densities remain similar. Chlorophyceae, while still the dominant group, are accompanied in these soils by Bacillariophyceae, Xanthophyceae, Eustigmatophyceae and Cyanophyceae. Total vegetation cover and thus light hitting the soil surface seems to be most important in determining the algal biomass. 相似文献
88.
The redlegged earth mite (Halotydeus destructor) and the blue oat mite (Penthaleus major) are major pests of pastures and crops in southern Australia. Reproductive modes, migration rates and levels of differentiation between populations were investigated using allozyme electrophoresis. Collections were made throughout Victoria and a sample was also obtained from Western Australia. Three enzyme loci were polymorphic in H. destructor (Mdh-1, Mdh-2 and Idh). Genotype frequencies of these loci did not differ between phenotypic males and females, providing no evidence for haplodiploidy. Allele frequencies were in Hardy-Weinberg equilibrium, indicating that H. destructor is diploid and sexual. This was confirmed via crosses between males and females. Allele frequencies differed between Victorian sites, although F statistics indicated little differentiation over all loci. A sample from Western Australia did not differ in allele frequencies from the Victorian sites. Four polymorphic loci were found in P. major (Mdh-1, Mdh-2, Idh and Gpi). Only a few multilocus genotypes occurred in a sample, indicating that P. major is parthenogenic. No male P. major were found in this study. A number of colour morphs were also identified and a genetic association between genital plate colour and clonal type was found in one population of P. major. Two different body colour morphs were associated with different clonal types. 相似文献
89.
The effect of adult learning through an oviposition experience, and pre-adult learning through development inside a host was
investigated in two strains of an Australian egg parasitoid,Trichogramma nrivelae (Hymenoptera: Trichogrammatidae). Host response was measured in two types of laboratory preference tests. In single host
tests, females reared on three lepidopteran hosts (Heliothis punctigera (Noctuidae),Papilio aegeus (Papilionidae), andHypolimnas bolina (Nymphalinae)) were presented host eggs individually, and allowed two ovipositions. Pre-adult experience affected host preference
in only one strain, while acceptance of a host was increased in both strains when they had previously oviposited in this host
species. An oviposition experience had a stronger effect on host preference than pre-adult experience. In choice tests, pairwise
combinations of hosts were arranged in an alternating grid. The ratio of host acceptances to host contacts was computed for
the whole test and up to the first oviposition. These indicated that effects of rearing host were weak or absent, but the
host chosen initially had a strong effect on host preference. Relative size of the hosts had a strong effect on choice of
the first host. The implications of learning inTrichogramma are discussed in relation to host preference testing procedures and the selection of candidate strains for mass rearing and
inundative release. 相似文献
90.
Summary To study the influence of phosphorylation and oxidation on the repeat domains of human Tau protein, we faced the challenge to selectively dimerize two cysteine-containing peptides in the presence of a nearby phosphate group. To this end, we were able to demonstrate the utility of a selective dimerization approach by forming disulfide bonds in unprotected phosphopeptides and extended the methodology to unprotected glycopeptides. Activation of one cysteine of a peptide chain with 2,2-dithiodipyridine and coupling this thiopyridyl-peptide to another peptide chain, containing an unprotected cysteine residue, yielded the mixed dimers in high purities and reasonable yields. Phosphate or sugar side chains on either peptide component remained unaffected during the activation and dimerization processes. While for mixed dimers the activated peptides were isolated by chromatography, homodimers were obtained by a simple one-pot reaction after 1 h. We demonstrate that cysteines can be dimerized in unprotected phosphopeptides and glycopeptides, without any side reactions affecting these posttranslational modifications.Abbreviations DCM
dichloromethane
- DMF
N,N-dimethylformamide
- DTP
2,2-dithiodipyridine
- Fmoc
9-fluorenylmethyloxycarbonyl
- HPLC
high-performance liquid chromatography
- MALDI
matrix-assisted laser desorption/ionization
- MS
mass spectrometry
- NFT
neurofibrillary tangles
- PHF
paired helical filaments
- PKC
protein kinase C
- RP
reversed phase
-
human Tau protein
- TFA
trifluoroacetic acid
Parts of this paper were presented at the 24th European Peptide Symposium in Edinburgh, Scotland, U.K., September 8–13, 1996. 相似文献