2,935 research outputs found
Attractive Interaction Between Pulses in a Model for Binary-Mixture Convection
Recent experiments on convection in binary mixtures have shown that the
interaction between localized waves (pulses) can be repulsive as well as {\it
attractive} and depends strongly on the relative {\it orientation} of the
pulses. It is demonstrated that the concentration mode, which is characteristic
of the extended Ginzburg-Landau equations introduced recently, allows a natural
understanding of that result. Within the standard complex Ginzburg-Landau
equation this would not be possible.Comment: 7 pages revtex with 3 postscript figures (uuencoded
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Pathways and Mechanisms that Prevent Genome Instability in Saccharomyces cerevisiae.
Genome rearrangements result in mutations that underlie many human diseases, and ongoing genome instability likely contributes to the development of many cancers. The tools for studying genome instability in mammalian cells are limited, whereas model organisms such as Saccharomyces cerevisiae are more amenable to these studies. Here, we discuss the many genetic assays developed to measure the rate of occurrence of Gross Chromosomal Rearrangements (called GCRs) in S. cerevisiae These genetic assays have been used to identify many types of GCRs, including translocations, interstitial deletions, and broken chromosomes healed by de novo telomere addition, and have identified genes that act in the suppression and formation of GCRs. Insights from these studies have contributed to the understanding of pathways and mechanisms that suppress genome instability and how these pathways cooperate with each other. Integrated models for the formation and suppression of GCRs are discussed
Bound Pairs of Fronts in a Real Ginzburg-Landau Equation Coupled to a Mean Field
Motivated by the observation of localized traveling-wave states (`pulses') in
convection in binary liquid mixtures, the interaction of fronts is investigated
in a real Ginzburg-Landau equation which is coupled to a mean field. In that
system the Ginzburg-Landau equation describes the traveling-wave amplitude and
the mean field corrsponds to a concentration mode which arises due to the
slowness of mass diffusion. For single fronts the mean field can lead to a
hysteretic transition between slow and fast fronts. Its contribution to the
interaction between fronts can be attractive as well as repulsive and depends
strongly on their direction of propagation. Thus, the concentration mode leads
to a new localization mechanism, which does not require any dispersion in
contrast to that operating in the nonlinear Schr\"odinger equation. Based on
this mechanism alone, pairs of fronts in binary-mixture convection are expected
to form {\it stable} pulses if they travel {\it backward}, i.e. opposite to the
phase velocity. For positive velocities the interaction becomes attractive and
destabilizes the pulses. These results are in qualitative agreement with recent
experiments. Since the new mechanism is very robust it is expected to be
relevant in other systems as well in which a wave is coupled to a mean field.Comment: 9 pages (RevTex), 9 figures (postscript
Phase shift of solutions of second order linear ordinary differential equations and related problems
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The properties of Msh2-Msh6 ATP binding mutants suggest a signal amplification mechanism in DNA mismatch repair.
DNA mismatch repair (MMR) corrects mispaired DNA bases and small insertion/deletion loops generated by DNA replication errors. After binding a mispair, the eukaryotic mispair recognition complex Msh2-Msh6 binds ATP in both of its nucleotide-binding sites, which induces a conformational change resulting in the formation of an Msh2-Msh6 sliding clamp that releases from the mispair and slides freely along the DNA. However, the roles that Msh2-Msh6 sliding clamps play in MMR remain poorly understood. Here, using Saccharomyces cerevisiae, we created Msh2 and Msh6 Walker A nucleotide-binding site mutants that have defects in ATP binding in one or both nucleotide-binding sites of the Msh2-Msh6 heterodimer. We found that these mutations cause a complete MMR defect in vivo The mutant Msh2-Msh6 complexes exhibited normal mispair recognition and were proficient at recruiting the MMR endonuclease Mlh1-Pms1 to mispaired DNA. At physiological (2.5 mm) ATP concentration, the mutant complexes displayed modest partial defects in supporting MMR in reconstituted Mlh1-Pms1-independent and Mlh1-Pms1-dependent MMR reactions in vitro and in activation of the Mlh1-Pms1 endonuclease and showed a more severe defect at low (0.1 mm) ATP concentration. In contrast, five of the mutants were completely defective and one was mostly defective for sliding clamp formation at high and low ATP concentrations. These findings suggest that mispair-dependent sliding clamp formation triggers binding of additional Msh2-Msh6 complexes and that further recruitment of additional downstream MMR proteins is required for signal amplification of mispair binding during MMR
Equipment for artificial intelligence
Issued as Final report, Project G-36-66
A computer memory for current events
Issued as Progress reports [1-2], and Final report, Project no. G-36-66
The role of experience in common sense and expert problem solving
Issued as Progress reports [nos. 1-5], Reports [nos. 1-6], and Final report, Project no. G-36-617 (includes Projects nos. GIT-ICS-87/26, GIT-ICS-85/19, and GIT-ICS-85/18
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