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61.
Summary A table presents the number of hours required for binding to reach 80% and 95% of the equilibrium value for a noncooperative, single site ligand binding system. A 2nd table provides the fraction of binding sites occupied and the fraction of the total ligand bound at equilibrium under the same conditions. 相似文献
62.
Tottey S Waldron KJ Firbank SJ Reale B Bessant C Sato K Cheek TR Gray J Banfield MJ Dennison C Robinson NJ 《Nature》2008,455(7216):1138-1142
Metals are needed by at least one-quarter of all proteins. Although metallochaperones insert the correct metal into some proteins, they have not been found for the vast majority, and the view is that most metalloproteins acquire their metals directly from cellular pools. However, some metals form more stable complexes with proteins than do others. For instance, as described in the Irving-Williams series, Cu(2+) and Zn(2+) typically form more stable complexes than Mn(2+). Thus it is unclear what cellular mechanisms manage metal acquisition by most nascent proteins. To investigate this question, we identified the most abundant Cu(2+)-protein, CucA (Cu(2+)-cupin A), and the most abundant Mn(2+)-protein, MncA (Mn(2+)-cupin A), in the periplasm of the cyanobacterium Synechocystis PCC 6803. Each of these newly identified proteins binds its respective metal via identical ligands within a cupin fold. Consistent with the Irving-Williams series, MncA only binds Mn(2+) after folding in solutions containing at least a 10(4) times molar excess of Mn(2+) over Cu(2+) or Zn(2+). However once MncA has bound Mn(2+), the metal does not exchange with Cu(2+). MncA and CucA have signal peptides for different export pathways into the periplasm, Tat and Sec respectively. Export by the Tat pathway allows MncA to fold in the cytoplasm, which contains only tightly bound copper or Zn(2+) (refs 10-12) but micromolar Mn(2+) (ref. 13). In contrast, CucA folds in the periplasm to acquire Cu(2+). These results reveal a mechanism whereby the compartment in which a protein folds overrides its binding preference to control its metal content. They explain why the cytoplasm must contain only tightly bound and buffered copper and Zn(2+). 相似文献
63.
A simple and inexpensive modification of the Kopf model 900 small animal stereotaxic instrument allows it to be used temporarily as a precision polyacrylamide slab gel slicer. 相似文献
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66.
A YAC-based physical map of the mouse genome. 总被引:9,自引:0,他引:9
C Nusbaum D K Slonim K L Harris B W Birren R G Steen L D Stein J Miller W F Dietrich R Nahf V Wang O Merport A B Castle Z Husain G Farino D Gray M O Anderson R Devine L T Horton W Ye X Wu V Kouyoumjian I S Zemsteva Y Wu A J Collymore D F Courtney J Tam M Cadman A R Haynes C Heuston T Marsland A Southwell P Trickett M A Strivens M T Ross W Makalowski Y Xu M S Boguski N P Carter P Denny S D Brown T J Hudson E S Lander 《Nature genetics》1999,22(4):388-393
A physical map of the mouse genome is an essential tool for both positional cloning and genomic sequencing in this key model system for biomedical research. Indeed, the construction of a mouse physical map with markers spaced at an average interval of 300 kb is one of the stated goals of the Human Genome Project. Here we report the results of a project at the Whitehead Institute/MIT Center for Genome Research to construct such a physical map of the mouse. We built the map by screening sequenced-tagged sites (STSs) against a large-insert yeast artificial chromosome (YAC) library and then integrating the STS-content information with a dense genetic map. The integrated map shows the location of 9,787 loci, providing landmarks with an average spacing of approximately 300 kb and affording YAC coverage of approximately 92% of the mouse genome. We also report the results of a project at the MRC UK Mouse Genome Centre targeted at chromosome X. The project produced a YAC-based map containing 619 loci (with 121 loci in common with the Whitehead map and 498 additional loci), providing especially dense coverage of this sex chromosome. The YAC-based physical map directly facilitates positional cloning of mouse mutations by providing ready access to most of the genome. More generally, use of this map in addition to a newly constructed radiation hybrid (RH) map provides a comprehensive framework for mouse genomic studies. 相似文献
67.
Sometimes a larger dataset needs to be reduced to just a few points, and it is desirable that these points be representative
of the whole dataset. If the future uses of these points are not fully specified in advance, standard decision-theoretic approaches
will not work. We present here methodology for choosing a small representative sample based on a mixture modeling approach. 相似文献
68.
Auxin regulates SCF(TIR1)-dependent degradation of AUX/IAA proteins. 总被引:46,自引:0,他引:46
69.
Repair of DNA double-strand breaks (DSBs) by homologous recombination requires resection of 5'-termini to generate 3'-single-strand DNA tails. Key components of this reaction are exonuclease 1 and the bifunctional endo/exonuclease, Mre11 (refs 2-4). Mre11 endonuclease activity is critical when DSB termini are blocked by bound protein--such as by the DNA end-joining complex, topoisomerases or the meiotic transesterase Spo11 (refs 7-13)--but a specific function for the Mre11 3'-5' exonuclease activity has remained elusive. Here we use Saccharomyces cerevisiae to reveal a role for the Mre11 exonuclease during the resection of Spo11-linked 5'-DNA termini in vivo. We show that the residual resection observed in Exo1-mutant cells is dependent on Mre11, and that both exonuclease activities are required for efficient DSB repair. Previous work has indicated that resection traverses unidirectionally. Using a combination of physical assays for 5'-end processing, our results indicate an alternative mechanism involving bidirectional resection. First, Mre11 nicks the strand to be resected up to 300 nucleotides from the 5'-terminus of the DSB--much further away than previously assumed. Second, this nick enables resection in a bidirectional manner, using Exo1 in the 5'-3' direction away from the DSB, and Mre11 in the 3'-5' direction towards the DSB end. Mre11 exonuclease activity also confers resistance to DNA damage in cycling cells, suggesting that Mre11-catalysed resection may be a general feature of various DNA repair pathways. 相似文献
70.