143,964 research outputs found
Recombinant DNA Molecules of Bacteriophage phi X174
phi X174 DNA structures containing two different parental genomes were detected genetically and examined by electron microscopy. These structures consisted of two monomeric double-stranded DNA molecules linked in a figure 8 configuration. Such DNA structures were observed to be formed preferentially in host recA+ cells or recA+ cell-free systems. Since the host recA+ allele is required for most phi X174 recombinant formation, we conclude that the observed figure 8 molecules are intermediates in, or end products of, a phi X174 recombination event. We propose that recombinant figure 8 DNA molecules arise as a result of "single-strand aggression," are stabilized by double-strand "branch migration," and represent a specific example of a common intermediate in genetic recombination
Deletion mutants of bacteriophage phiX174
Mutants of bacteriophage phiX174 have been isolated that are less dense than wild-type phiX particles in CsCl. When mutant viral (+) strand DNA and wild-type complementary (-) strand DNA are hybridized, the resulting duplex molecules have single-stranded loops characteristic of wild-type-deletion heteroduplexes. The mutant bacteriophages fail to complement phiX amber mutants in cistron E. We conclude that the mutant viruses have deleted approximately 7% of the phiX genome in the region of cistron E
Mitochondrial ribosome assembly in Neurospora. Structural analysis of mature and partially assembled ribosomal subunits by equilibrium centrifugation in CsCl gradients
In Neurospora, one protein associated with the mitochondrial small ribosomal subunit (S-5, Mr 52,000) is synthesized intramitochondrially and is assumed to be encoded by mtDNA. When mitochondrial protein synthesis is inhibited, either by chloramphenicol or by mutation, cells accumulate incomplete mitochondrial small subunits (CAP-30S and INC-30S particles) that are deficient in S-5 and several other proteins. To gain additional insight into the role of S-5 in mitochondrial ribosome assembly, the structures of Neurospora mitochondrial ribosomal subunits, CAP-30S particles, and INC-30S particles were analyzed by equilibrium centrifugation in CsCl gradients containing different concentrations of Mg+2. The results show (a) that S-5 is tightly associated with small ribosomal subunits, as judged by the fact that it is among the last proteins to be dissociated in CsCl gradients as the Mg+2 concentration is decreased, and (b) that CAP-30S and INC-30S particles, which are deficient in S-5, contain at most 12 proteins that are bound as tightly as in mature small subunits. The CAP-30S particles isolated from sucrose gradients contain a number of proteins that appear to be loosely bound, as judged by dissociation of these proteins in CsCl gradients under conditions in which they remain associated with mature small subunits. The results suggest that S-5 is required for the stable binding of a subset of small subunit ribosomal proteins
A proof of the Gutzwiller Semiclassical Trace Formula using Coherent States Decomposition
The Gutzwiller semiclassical trace formula links the eigenvalues of the
Scrodinger operator ^H with the closed orbits of the corresponding classical
mechanical system, associated with the Hamiltonian H, when the Planck constant
is small ("semiclassical regime"). Gutzwiller gave a heuristic proof, using the
Feynman integral representation for the propagator of ^H. Later on
mathematicians gave rigorous proofs of this trace formula, under different
settings, using the theory of Fourier Integral Operators and Lagrangian
manifolds. Here we want to show how the use of coherent states (or gaussian
beams) allows us to give a simple and direct proof.Comment: 17 pages, LaTeX, available on http://qcd.th.u-psud.f
Limitations on wind-tunnel pressure signature extrapolation
Analysis of some recent experimental sonic boom data has revived the hypothesis that there is a closeness limit to the near-field separation distance from which measured wind tunnel pressure signatures can be extrapolated to the ground as though generated by a supersonic-cruise aircraft. Geometric acoustic theory is used to derive an estimate of this distance and the sample data is used to provide a preliminary indication of practical separation distance values
Hyperbolic Multi-Monopoles With Arbitrary Mass
On a complete manifold, such as Euclidean 3-space or hyperbolic 3-space, the
limit at infinity of the norm of the Higgs field is called the mass of the
monopole. We show the existence, on hypebolic 3-space, of monopoles with given
magnetic charge and arbitrary mass. Previously, aside from charge one
monopoles, existence was known only for monopoles with integral mass (since
these arise from U(1) invariant instantons on Euclidean 4-space). The method of
proof is based on Taubes' gluing procedure, using well-separated, explicit,
charge one monopoles. The analysis is carried out in a weighted Sobolev space
and necessitates eliminating the possibility of point spectra.Comment: 20 page
- …