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121.
122.
A novel allele of Saccharomyces cerevisiae RFA1 that is deficient in recombination and repair and suppressible by RAD52. 总被引:8,自引:2,他引:6
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To understand the mechanisms involved in homologous recombination, we have performed a search for Saccharomyces cerevisiae mutants unable to carry out plasmid-to-chromosome gene conversion. For this purpose, we have developed a colony color assay in which recombination is induced by the controlled delivery of double-strand breaks (DSBs). Recombination occurs between a chromosomal mutant ade2 allele and a second plasmid-borne ade2 allele where DSBs are introduced via the site-specific HO endonuclease. Besides isolating a number of new alleles in known rad genes, we identified a novel allele of the RFA1 gene, rfa1-44, which encodes the large subunit of the heterotrimeric yeast single-stranded DNA-binding protein RPA. Characterization of rfa1-44 revealed that it is, like members of the RAD52 epistasis group, sensitive to X rays, high doses of UV, and HO-induced DSBs. In addition, rfa1-44 shows a reduced ability to undergo sporulation and HO-induced gene conversion. The mutation was mapped to a single-base substitution resulting in an aspartate at amino acid residue 77 instead of glycine. Moreover, all radiation sensitivities and repair defects of rfa1-44 are suppressed by RAD52 in a dose-dependent manner, and one RAD52 mutant allele, rad52-34, displays nonallelic noncomplementation when crossed with rfa1-44. Presented is a model accounting for this genetic interaction in which Rfa1, in a complex with Rad52, serves to assemble other proteins of the recombination-repair machinery at the site of DSBs and other kinds of DNA damage. We believe that our findings and those of J. Smith and R. Rothstein (Mol. Cell. Biol. 15:1632-1641, 1995) are the first in vivo demonstrations of the involvement of a eukaryotic single-stranded binding protein in recombination and repair processes. 相似文献
123.
Self-electrophoresis is not the mechanism for motility in swimming cyanobacteria. 总被引:3,自引:1,他引:2
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Swimming cyanobacteria do not have flagella. In principle, they could be propelled by streams of ions flowing from head to tail, i.e., by a self-electrophoretic mechanism. We have ruled out this possibility by showing that cells of a swimming Synechococcus species fail to drift in an external electric field. 相似文献
124.
Insertional mutagenesis screens using the P[lacZ, rosy(+)] (PZ) transposable element have provided thousands of mutant lines for analyzing genes of varied function in the fruitfly, Drosophila melanogaster. As has been observed with other P elements, many of the PZ-induced mutations result from insertion of the P element into the promoter or 5'' untranslated regions of the affected gene. We document here a novel mechanism for mutagenesis by this element. We show that sequences present within the element direct aberrant splicing and termination events that produce a mRNA composed of 5'' sequences from the mutated gene (in this case, pipsqueak) and 3'' sequences from within the P[lacZ, rosy(+)] element. These truncated RNAs could yield proteins with dominant mutant effects. 相似文献
125.
Regulation of expression of a cDNA from barley roots encoding a high affinity sulphate transporter 总被引:27,自引:3,他引:24
Frank W. Smith Malcolm J. Hawkesford Paul M. Ealing David T. Clarkson Peter J. Vanden Berg Ann R. Belcher Andrew G.S. Warrilow 《The Plant journal : for cell and molecular biology》1997,12(4):875-884
A cDNA encoding a high-affinity sulphate transporter has been isolated from barley by complementation of a yeast mutant. The cDNA, designated HVST1, encodes a polypeptide of 660 amino acids (Mr = 72 550), which is predicted to have 12 membrane-spanning domains and has extensive sequence homology with other identified eukaryotic sulphate transporters. The Km for sulphate was 6.9 µM when the HVST1 cDNA was expressed in a yeast mutant deficient in the gene encoding for the yeast SUL1 sulphate transporter. The strong pH-dependency of sulphate uptake when HVST1 was expressed heterologously in yeast suggests that the HVST1 polypeptide is a proton/sulphate co-transporter. The gene encoding HVST1 is expressed specifically in root tissues and the abundance of the mRNA is strongly influenced by sulphur nutrition. During sulphur-starvation of barley, the abundance of mRNA corresponding to HVST1, and the capacity of the roots to take up sulphate, both increase. Upon re-supply of sulphate, the abundance of the mRNA corresponding to HVST1, and the capacity of the roots to take up sulphate, decrease rapidly, concomitant with rises in tissue sulphate, cysteine and glutathione contents. Addition of the cysteine precursor, O-acetylserine, to plants grown with adequate sulphur supply, leads to increases in sulphate transporter mRNA, sulphate uptake rates and tissue contents of glutathione and cysteine. It is suggested, that whilst sulphate, cysteine and glutathione may be candidates for negative metabolic regulators of sulphate transporter gene expression, this regulation may be overridden by O-acetylserine acting as a positive regulator. 相似文献
126.
Lower limb skeletal muscle function after 6wk of bed rest 总被引:7,自引:0,他引:7
Berg, H. E., L. Larsson, and P. A. Tesch. Lower limbskeletal muscle function after 6 wk of bed rest. J. Appl. Physiol. 82(1): 182-188, 1997.Force,electromyographic (EMG) activity, muscle mass, and fibercharacteristics were studied in seven healthy men before and after 6 wkof bed rest. Maximum voluntary isometric and concentric knee extensortorque decreased (P < 0.05)uniformly across angular velocities by 25-30% after bed rest.Maximum quadricep rectified EMG decreased by 19 ± 23%, whereassubmaximum (100-Nm isometric action) EMG increased by 44 ± 28%.Knee extensor muscle cross-sectional area (CSA), assessed by usingmagnetic resonance imaging, decreased by 14 ± 4%. Maximum torqueper knee extensor CSA decreased by 13 ± 9%. Vastus lateralis fiberCSA decreased 18 ± 14%. Neither type I, IIA, and IIB fiberpercentages nor their relative proportions of myosin heavy chain (MHC)isoforms were altered after bed rest. Because the decline in strengthcould not be entirely accounted for by decreased muscle CSA, it issuggested that the strength loss is also due to factors resulting indecreased neural input to muscle and/or reduced specifictension of muscle, as evidenced by a decreased torque/EMG ratio.Additionally, it is concluded that muscle unloading in humans does notinduce important changes in fiber type or MHC composition or in vivomuscle contractile properties. 相似文献
127.
A Gly1127Ser mutation in an EGF-like domain of the fibrillin-1 gene is a risk factor for ascending aortic aneurysm and dissection.
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U Francke M A Berg K Tynan T Brenn W Liu T Aoyama C Gasner D C Miller H Furthmayr 《American journal of human genetics》1995,56(6):1287
Ascending aortic disease, ranging from mild aortic root enlargement to aneurysm and/or dissection, has been identified in 10 individuals of a kindred, none of whom had classical Marfan syndrome (MFS). Single-strand conformation analysis of the entire fibrillin-1 (FBN1) cDNA of an affected family member revealed a G-to-A transition at nucleotide 3379, predicting a Gly1127Ser substitution. The glycine in this position is highly conserved in EGF-like domains of FBN1 and other proteins. This mutation was present in 9 of 10 affected family members and in 1 young unaffected member but was not found in other unaffected members, in 168 chromosomes from normal controls, and in 188 chromosomes from other individuals with MFS or related phenotypes. FBN1 intragenic marker haplotypes ruled out the possibility that the other allele played a significant role in modulating the phenotype in this family. Pulse-chase studies revealed normal fibrillin synthesis but reduced fibrillin deposition into the extracellular matrix in cultured fibroblasts from a Gly1127Ser carrier. We postulate that the Gly1127Ser FBN1 mutation is responsible for reduced matrix deposition. We suggest that mutations such as this one may disrupt EGF-like domain folding less drastically than do substitutions of cysteine or of other amino acids important for calcium-binding that cause classical MFS. The Gly1127Ser mutation, therefore, produces a mild form of autosomal dominantly inherited weakness of elastic tissue, which predisposes to ascending aortic aneurysm and dissection later in life. 相似文献
128.
Production of a Novel Extracellular Polysaccharide by Lactobacillus sake 0-1 and Characterization of the Polysaccharide 总被引:4,自引:1,他引:3
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D. van den Berg G. W. Robijn A. C. Janssen M. Giuseppin R. Vreeker J. P. Kamerling J. Vliegenthart A. M. Ledeboer C. T. Verrips 《Applied microbiology》1995,61(8):2840-2844
A novel exopolysaccharide (EPS) produced by Lactobacillus sake 0-1 (CBS 532.92) has been isolated and characterized. When the strain was grown on glucose, the produced EPS contained glucose and rhamnose in a molar ratio of 3:2 and the average molecular mass distribution (M(infm)) was determined at 6 x 10(sup6) Da. At a concentration of 1%, the 0-1 EPS had better viscosifying properties than xanthan gum when measured over a range of shear rates from 0 to 300 s(sup-1), while shear-thinning properties were comparable. Rheological data and anion-exchange chromatography suggested the presence of a negatively charged group in the EPS. Physiological parameters for optimal production of EPS were determined in batch fermentation experiments. Maximum EPS production was 1.40 g (middot) liter(sup-1), which was obtained when L. sake 0-1 had been grown anaerobically at 20(deg)C and pH 5.8. When cultured at lower temperatures, the EPS production per gram of biomass increased from 600 mg at 20(deg)C to 700 mg at 10(deg)C but the growth rate in the exponential phase decreased from 0.16 to 0.03 g (middot) liter(sup-1) (middot) h(sup-1). EPS production started in the early growth phase and stopped when the culture reached the stationary phase. Growing the 0-1 strain on different energy sources such as glucose, galactose, mannose, fructose, lactose, and sucrose did not alter the composition of the EPS produced. 相似文献
129.
K. S. Boo K. C. Park D. R. Hall A. Cork B. G. Berg H. Mustaparta 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1995,177(6):695-699
The behavioural significance of (Z)-9-tetradecenal to male H. assulta was tested by comparing the number of moths attracted to lures containing a standard synthetic female sex pheromone with lures in which (Z)-9-tetradecenal was also added. The standard pheromone mixture used contained 1000 g (Z)-9-hexadecenal, 50 g (Z)-11-hexadecenal, 300 g (Z)-9-hexadecenyl acetate and 15 g (Z)-11-hexadecenyl acetate impregnated on rubber septa. Addition of (Z)-9-tetradecenal to the standard pheromone was shown to significantly reduce the caught of male H. assulta when added in amounts greater than 10 g or 1% of the major pheromone component in both field and net-house experiments. The reduction in catch was found to be dependent on the quantity of (Z)-9-tetradecenal added to the standard pheromone. The implications of these results on conspecific and inter-specific pheromone-mediated communication in H. assulta and related sympatric heliothine species is discussed.Abbreviations
Z9-16:AL
(Z)-9-hexadecenal
-
Z11-16:AL
(Z)-11-hexadecenal
-
Z9-16:AC
(Z)-9-hexadecenyl acetate
-
Z11-16:AC
(Z)-11-hexadecenyl acetate
-
Z9-14:AL
(Z)-9-tetradecenal
-
Z9-16:OH
(Z)-9-hexadecen-1-ol
-
Z11-16:OH
(Z)-11-hexadecen-1-ol
- RH
relative humidity 相似文献
130.
Neville Marks Martin J. Berg Abba J. Kastin David H. Coy 《Neurochemistry international》1984,6(3):347-353
N-Tyr-MIF-1 (Tyr-Pro-Leu-Gly·NH2), an immunoreactive neuropeptide exhibiting saturable high affinity binding in rat brain was found to be converted into MIF-1 (Pro-Leu-Gly·NH2) by a specific brain aminopeptidase present in rat brain homogenates or cytosol, but with low activity associated with synaptosomal plasma membranes and microsomes. Conversion occurred at a rate of 16 μmol per g w/wt per h and was unaffected by puromycin but inhibited by bestatin (I50, 5 × 10?5 M). Aminopeptidases purified from cytosolic fractions of rat brain (arylamidase), mouse brain (Mn2+-activated aminopeptidase) or porcine kidney (leucine aminopeptidase) were inactive towards N-Tyr-MIF-1 but degraded MIF-1 with release of Leu-Gly·NH2 as detected by RP-HPLC procedures. Morphiceptin (Tyr-Pro-Phe-Pro·NH2), a μ opioid agonist, also acted as a substrate for the N-Tyr-MIF-1 converting enzyme with cleavage of the Tyr-Pro bond. These tetrapeptides, but not MIF-1 or its N-blocked analogs, were degraded in vitro by a metalloendopeptidase purified from kidney membranes. Since dipeptide products were not detected for crude extracts, a significant role for brain metalloendopeptidase on turnover can be excluded. Thus the results point to the presence of a specific (X-Pro-degrading) aminopeptidase in brain cytosol as an enzyme responsible for converting N-Tyr-MIF-1 and inactivating morphiceptin. 相似文献