272,015 research outputs found
Transcriptionally inactive oocyte-type 5S RNA genes of Xenopus laevis are complexed with TFIIIA in vitro
An extract from whole oocytes of Xenopus laevis was shown to transcribe somatic-type 5S RNA genes approximately 100-fold more efficiently than oocyte-type 5S RNA genes. This preference was at least 10-fold greater than the preference seen upon microinjection of 5S RNA genes into oocyte nuclei or upon in vitro transcription in an oocyte nuclear extract. The approximately 100-fold transcriptional bias in favor of the somatic-type 5S RNA genes observed in vitro in the whole oocyte extract was similar to the transcriptional bias observed in developing Xenopus embryos. We also showed that in the whole oocyte extract, a promoter-binding protein required for 5S RNA gene transcription, TFIIIA, was bound both to the actively transcribed somatic-type 5S RNA gene and to the largely inactive oocyte-type 5S RNA genes. These findings suggest that the mechanism for the differential expression of 5S RNA genes during Xenopus development does not involve differential binding of TFIIIA to 5S RNA genes
Measurement of B[Y(5S)->Bs(*) anti-Bs(*)] Using phi Mesons
Knowledge of the Bs decay fraction of the Y(5S) resonance, fs, is important
for Bs meson studies at the Y(5S) energy. Using a data sample collected by the
CLEO III detector at CESR consisting of 0.423/fb on the Y(5S) resonance,
6.34/fb on the Y(4S) and 2.32/fb in the continuum below the Y(4S), we measure
B(Y(5S) -> phi X)=(13.8 +/- 0.7 {+2.3}{-1.5})% and B(Y(4S) -> phi X) = (7.1 +/-
0.1 +/-0.6)%; the ratio of the two rates is (1.9 +/- 0.1 {+0.3}{-0.2}). This is
the first measurement of the phi meson yield from the Y(5S). Using these rates,
and a model dependent estimate of B(Bs -> phi X), we determine fs = (24.6 +/-
2.9 {+11.0}{-5.3})%. We also update our previous independent measurement of fs
made using the inclusive Ds yields to now be (16.8 +/- 2.6 {+6.7}{-3.4)%, due
to a better estimate of the number of hadronic events. We also report the total
Y(5S) hadronic cross section above continuum to be sigma(e^+e^- ->
Y(5S))=(0.301 +/- 0.002 +/- 0.039) nb. This allows us to extract the fraction
of B mesons as (58.9+/-10.0+/-9.2)%, equal to 1-fs. averaging the three methods
gives a model dependent result of fs=(21 {+6}{-3})%.Comment: 23 pages postscript,also available through
http://www.lns.cornell.edu/public/CLNS/2006/, Submitted to PR
Relativistic calculations of quasi-one-electron atoms and ions using Laguerre and Slater spinors
A relativistic description of the structure of heavy alkali atoms and
alkali-like ions using S-spinors and L-spinors has been developed. The core
wavefunction is defined by a Dirac-Fock calculation using an S-spinors basis.
The S-spinor basis is then supplemented by a large set of L-spinors for the
calculation of the valence wavefunction in a frozen-core model. The numerical
stability of the L-spinor approach is demonstrated by computing the energies
and decay rates of several low-lying hydrogen eigenstates, along with the
polarizabilities of a hydrogenic ion. The approach is then applied to
calculate the dynamic polarizabilities of the , and states of
Sr. The magic wavelengths at which the Stark shifts between different pairs
of transitions are zero are computed. Determination of the magic wavelengths
for the and transitions near
~nm (near the wavelength for the transitions) would allow a
determination of the oscillator strength ratio for the
and transitions.Comment: 2 figures, 23 page
Functional characterization of synthetic leukotriene B and its stereochemical isomers.
Leukotriene B (LTB), a potent lipid chemotactic factor for neutrophils, is 5S,12R-dihydroxy-6,14-cis,8,10-trans-eicosatetraenoic acid (Fig 1), based upon direct comparison of natural LTB with synthetic 5S,12R-dihydroxy-6,8,10,14-eicosatetraenoic acid (5,12-di-HETE) stereoisomers in three biological assays. Of the six synthetic stereoisomers evaluated, only the 5S,12R,6,14-cis,8,10-trans compound had chemotactic potency for human neutrophils in vitro that was comparable to that of natural LTB, with a concentration of 3 X 10(9-9) M eliciting a one-half maximum response. In contrast, the racemic mixture of 5R,12R- and 5S,12S-6,10-trans,8,14-cis, the racemic mixture of 5S,12R- and 5R,12S-6,10-trans,8,14-cis, the 5S,12R-6,8-trans,10,14-cis, the 5S,12R-6,8,10-trans,14-cis, and the 5S,12S-6,8,10-trans,14-cis stereoisomers required concentrations of 3 X 10(-7) to 1 X 10(-6) M to elicit comparable responses. Only natural LTB and its synthetic counterpart elicited a local neutrophil infiltration when injected into the skin of the rhesus monkey at 10 ng and 100 ng per site. Natural and synthetic LTB at a concentration of 3 X 10(-8) M each provoked an EC25 contractile response of guinea pig pulmonary parenchymal strips in vitro, whereas the other four tested stereoisomers of 5,12-di-HETE were inactive at this concentration. Structure-function analyses suggest that the neutrophil chemotactic activity depends critically upon the C-1 to C-12 domain, including the stereochemistry of the 6-,8-,and 10-olefinic bonds and the presence of both hydroxyl groups
- …