Electrostatic potential in a superconductor

The electrostatic potential in a superconductor is studied. To this end Bardeen's extension of the Ginzburg-Landau theory to low temperatures is used to derive three Ginzburg-Landau equations - the Maxwell equation for the vector potential, the Schroedinger equation for the wave function and the Poisson equation for the electrostatic potential. The electrostatic and the thermodynamic potential compensate each other to a great extent resulting into an effective potential acting on the superconducting condensate. For the Abrikosov vortex lattice in Niobium, numerical solutions are presented and the different contributions to the electrostatic potential and the related charge distribution are discussed.Comment: 19 pages, 11 figure

Substrate-leash amplification with ribonuclease S-peptide and S-protein.

Abstract The S-peptide and S-protein fragments of ribonuclease S (RNase S, no EC no. assigned) have been immobilized onto separate Sepharose gels via a "leash" of polycytidylic acid substrate. Each of these gels releases its RNase fragment when treated with the complementary enzyme fragment or with RNase A (EC 3.1.27.5), and the released fragments recombine to give RNase S activity. Thus this system provides substrate-leash amplification (SLA), such that more enzymatic activity is eluted from the system than is applied. For example, 100 pg of RNase applied to the S-peptide gel is amplified by 1.9 X 10(4) to the equivalent of 1.9 micrograms of activity in 20 h, when followed by combination of the released S-peptide with excess S-protein. We also tested a three-stage amplification system, with a pair of S-peptide and S-protein gels at each stage. In this system the cumulative amplification of the initial 1-ng dose of RNase A is 4.9, 52, and 25-fold after each stage, respectively. Only 2 mg of each SLA gel is used per stage in these experiments, reflecting the magnitude of their production of RNase S activity.</jats:p

G-quadruplex recognition activities of <it>E. Coli</it> MutS

<p>Abstract</p> <p>Background</p> <p>Guanine quadruplex (G4 DNA) is a four-stranded structure that contributes to genome instability and site-specific recombination. G4 DNA folds from sequences containing tandemly repetitive guanines, sequence motifs that are found throughout prokaryote and eukaryote genomes. While some cellular activities have been identified with binding or processing G4 DNA, the factors and pathways governing G4 DNA metabolism are largely undefined. Highly conserved mismatch repair factors have emerged as potential G4-responding complexes because, in addition to initiating heteroduplex correction, the human homologs bind non-B form DNA with high affinity. Moreover, the MutS homologs across species have the capacity to recognize a diverse range of DNA pairing variations and damage, suggesting a conserved ability to bind non-B form DNA.</p> <p>Results</p> <p>Here, we asked if <it>E. coli</it> MutS and a heteroduplex recognition mutant, MutS F36A, were capable of recognizing and responding to G4 DNA structures. We find by mobility shift assay that <it>E. coli</it> MutS binds to G4 DNA with high affinity better than binding to G-T heteroduplexes. In the same assay, MutS F36A failed to recognize G-T mismatched oligonucleotides, as expected, but retained an ability to bind to G4 DNA. Association with G4 DNA by MutS is not likely to activate the mismatch repair pathway because nucleotide binding did not promote release of MutS or MutS F36A from G4 DNA as it does for heteroduplexes. G4 recognition activities occur under physiological conditions, and we find that M13 phage harboring G4-capable DNA poorly infected a MutS deficient strain of <it>E. coli</it> compared to M13mp18, suggesting functional roles for mismatch repair factors in the cellular response to unstable genomic elements.</p> <p>Conclusions</p> <p>Taken together, our findings demonstrate that <it>E. coli</it> MutS has a binding activity specific for non-B form G4 DNA, but such binding appears independent of canonical heteroduplex repair activation.</p