U6 spliceosomal RNA has a complex secondary structure that includes a highly conserved stemloop near the 3' end. The 3' stem is unwound when U6 RNA base-pairs with U4 RNA during spliceosome assembly, ...but likely reforms when U4 RNA leaves the spliceosome prior to the catalysis of splicing. A mutation in yeast U6 RNA that hyperstabilizes the 3' stem confers cold sensitivity and inhibits U4/U6 assembly as well as a later step in splicing. Here we show that extragenic suppressors of the 3' stem mutation map to the gene coding for splicing factor Prp24. The suppressor mutations are located in the second and third of three RNA-recognition motifs (RRMs) in Prp24 and are predicted to disrupt RNA binding. Mutations in U6 RNA predicted to destabilize a novel helix adjacent to the 3' stem also suppress the 3' stem mutation and enhance the growth defect of a suppressor mutation in RRM2 of Prp24. Both phenotypes are reverted by a compensatory mutation that restores pairing in the novel helix. These results are best explained by a model in which RRMs 2 and 3 of Prp24 stabilize an extended intramolecular structure in U6 RNA that competes with the U4/U6 RNA interaction, and thus influence both association and dissociation of U4 and U6 RNAs during the splicing cycle.
We present a measurement of the W boson production charge asymmetry in p$\bar{p}$→W+X→eν+X events at a center of mass energy of 1.96 TeV, using 9.7 fb-1 of integrated luminosity collected with the D0 ...detector at the Fermilab Tevatron Collider. The neutrino longitudinal momentum is determined by using a neutrino weighting method, and the asymmetry is measured as a function of the W boson rapidity. The measurement extends over wider electron pseudorapidity region than previous results and is the most precise to date, allowing for precise determination of proton parton distribution functions in global fits.
Rivers and streams are among the most threatened ecosystems worldwide, and their fish assemblages have been modified by anthropogenic habitat alteration and introductions of non-native species. ...Consequently, two frequently observed patterns of assemblage change over time are species loss and biotic homogenization. In the present study, we compared contemporary (2006—2007) and historical (1948—1955) assemblages of darters, a group of small benthic fishes of the family Percidae, in the Arkansas River drainage of northeastern Oklahoma, USA. Results showed species loss between the two sampling periods, with historical estimates of overall species diversity across the study area exceeding contemporary estimates by five to eight species. Assemblages showed a low degree of darter similarity based on species presence and absence, with pairwise site comparisons (Jaccard's similarity index) between historical and contemporary samples averaging < 0.35. No significant homogenization or differentiation of assemblages occurred. Range expansion of widespread species, one of the primary mechanisms of biotic homogenization, was not observed; rather, all species occurred at a smaller proportion of sites in contemporary samples. Our results highlight the threat posed by anthropogenic habitat alteration to taxonomic groups such as darters, most of which are habitat specialists. However, our results suggest that biotic homogenization is unlikely to occur in the absence of immigration, especially if assemblages are subjected to 'novel disturbances' such as dam construction and watershed-scale habitat degradation which negatively affect all components of the assemblage.
We study the production of the exotic charged charmoniumlike state Z(c)(+/-)(3900) in p (p) over bar collisions through the sequential process psi(4260) -> Z(c)(+/-)(3900)(pi)(-/+), ...Z(c)(+/-)(3900) -> J/psi pi(+/-). Using the subsample of candidates originating from semi-inclusive weak decays of b-flavored hadrons, we measure the invariant mass and natural width to be M = 3902.6(-5.0)(+5.2)(stat)(-1.4)(+3.3)(syst) MeV and Gamma = 32(-21)(+28)(stat)(-7)(+26)(syst) MeV, respectively. We search for prompt production of the Z(c)(+/-)(3900) through the same sequential process. No significant signal is observed, and we set an upper limit of 0.70 at the 95% credibility level on the ratio of prompt production to the production via b-hadron decays. The study is based on 10.4 fb(-1) of p (p) over bar collision data collected by the D0 experiment at the Fermilab Tevatron collider.
We present a study of the normalized transverse momentum distribution of W bosons produced in p (p) over bar collisions, using data corresponding to an integrated luminosity of 4.35 fb(-1) collected ...with the D0 detector at the Fermilab Tevatron collider at root s = 1.96 TeV. The measurement focuses on the transverse momentum region below 15 GeV, which is of special interest for electroweak precision measurements; it relies on the same detector calibration methods which were used for the precision measurement of the W boson mass. The measured distribution is compared to different QCD predictions and a procedure is given to allow the comparison of any further theoretical models to the D0 data.
We present a study of the normalized transverse momentum distribution of W bosons produced in $p\bar{p}$ collisions, using data corresponding to an integrated luminosity of 4.35 fb-1 collected with ...the D0 detector at the Fermilab Tevatron collider at $\sqrt{s}$ = 1.96 TeV. The measurement focuses on the transverse momentum region below 15 GeV, which is of special interest for electroweak precision measurements; it relies on the same detector calibration methods which were used for the precision measurement of the W boson mass. The measured distribution is compared to different QCD predictions and a procedure is given to allow the comparison of any further theoretical models to the D0 data.
We measure the mass of the top quark in lepton + jets final states using the full sample of p (p) over bar collision data collected by the D0 experiment in Run II of the Fermilab Tevatron Collider at ...root s = 1.96 TeV, corresponding to 9.7 fb(-1) of integrated luminosity. We use a matrix element technique that calculates the probabilities for each event to result from t (t) over bar production or background. The overall jet energy scale is constrained in situ by the mass of theW boson. We measure m(t) = 174.98 +/- 0.76 GeV. This constitutes the most precise single measurement of the top-quark mass.
We present a measurement of top quark polarization in tt¯ pair production in pp¯ collisions at s=1.96 TeV using data corresponding to 9.7 fb−1 of integrated luminosity recorded with the D0 detector ...at the Fermilab Tevatron Collider. We consider final states containing a lepton and at least three jets. The polarization is measured through the distribution of lepton angles along three axes: the beam axis, the helicity axis, and the transverse axis normal to the tt¯ production plane. This is the first measurement of top quark polarization at the Tevatron using lepton+jet final states and the first measurement of the transverse polarization in tt¯ production. The observed distributions are consistent with standard model predictions of nearly no polarization.
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