The DNA topoisomerases are ubiquitous enzymes that fulfil vital roles in the replication, transcription and recombination of DNA by carrying out DNA-strand passage reactions. Here we characterize a ...prokaryotic counterpart to the eukaryotic topoisomerase I in the hyperthermophilic methanogen Methanopyrus kandleri. The new enzyme, called topoisomerase V, has the following properties in common with eukaryotic topoisomerase I, which distinguish it from all other known prokaryotic topoisomerases: (1) its activity is Mg(2+)-independent; (2) it relaxes both negatively and positively supercoiled DNA; (3) it makes a covalent complex with the 3' end of the broken DNA strand; and (4) it is recognized by antibody raised against human topoisomerase I. Eukaryotic-like enzymes have been discovered in some hyperthermophilic prokaryotes, namely the eocytes and the extremely thermophilic archaebacteria, and hyperthermophilic homologues of eukaryotic DNA polymerase-alpha, transcription factor IIB and DNA ligase have all been reported. Thus our findings support the idea that some essential parts of the eukaryotic transcription-translation and replication machineries were in place before the emergence of eukaryotes, and that the closest living relatives of eukaryotes may be hyperthermophiles.
OBJECTIVES--Vietnamese immigration to the U.S. since the conclusion of the Vietnam war has been substantial and in Orange County, CA, Vietnamese Americans comprise 3% of the population (the largest ...community in the US). Our objective was to collect data on the HIV/AIDS knowledge, attitudes and self-reported high risk behaviours within this community. METHODS--A survey instrument was administered anonymously in Vietnamese to 532 respondents in their homes. Individuals from three population strata were randomly sampled: men 18 to 35 years old (N = 193); men 36 to 45 years old (N = 137); and women 18 to 35 years old (N = 202). Data were gathered on: (1) degree of acculturation; (2) knowledge and attitudes towards HIV/AIDS; and (3) self-reported sexual and other high risk practices. RESULTS--Survey data indicated that 38% of respondents were very worried about themselves and 83% were worried about a family member getting AIDS. Knowledge about actual modes of HIV transmission was generally accurate, but a substantial minority still believed that HIV can be transmitted through casual contact, and 68% from needles used in hospitals. Women demonstrated less accurate knowledge than men on five key items. Quarantine of the HIV infected was agreed to by 45%. Twenty-nine percent did not believe that the epidemic would affect them personally, and 49% stated that they did not have enough information about AIDS to protect themselves. Regarding sexual practices, 31% reported never having had sex. Of the others, 8% had two or more sexual partners in the prior 12 months. No same sex behaviour was reported. Six percent of men had visited a female prostitute; of these, 24% had visited 2 or more in the prior 12 months; half of encounters in this time period were outside the US. Substantial percentages of sexually active, unmarried respondents indicated that they never use (17-40%) or only sometimes use (10-32%) condoms. Less than 1% had used injection drugs. CONCLUSIONS--Education should be targeted at the Vietnamese community of southern California to improve knowledge that HIV cannot be contracted through casual contact, to convey information about methods for self-protection, and to reduce high risk sexual practices such as unprotected sex, sex with multiple partners and sex with prostitutes.
The nine-membered -Cu(II)-N-N-(3) ring of trimeric copper-pyrazolato complexes provides a sturdy framework on which water is twice deprotonated in consecutive steps, forming mu(3)-OH and mu(3)-O ...species. In the presence of excess chlorides the mu(3)-O(H) ligand is replaced by two mu(3)-Cl ions. The interconversion of mu(3)-OH and mu(3)-O and the exchange of mu(3)-O(H) and mu(3)-Cl are reversible, and the three species involved have been structurally characterized: PPNCu(3)(mu(3)-OH)(mu-pz)(3)Cl(3)(thf).CH(2)Cl(2) (1a), monoclinic P2(1)/n, a = 10.055(2) A, b = 35.428(5) A, c = 15.153(2) A, beta = 93.802(3) degrees, V = 5386(1) A(3), Z = 4; Bu(4)NCu(3)(mu(3)-OH)(mu-pz)(3)Cl(3) (1b), triclinic P-1, a = 9.135(2) A, b = 13.631(2) A, c = 14.510(2) A, alpha = 67.393(2) degrees, beta = 87.979(2) degrees, gamma = 80.268(3) degrees, V = 1643.2(4) A(3), Z = 2; PPN(2)Cu(3)(mu(3)-O)(mu-pz)(3)Cl(3) (2), monoclinic P2/c, a = 12.807(2) A, b = 13.093(2) A, c = 23.139(4) A, beta = 105.391(3) degrees, V = 3741(1) A(3), Z = 2; PPN(2)Cu(3)(mu(3)-Cl)(2)(mu-pz)(3)Cl(3).0.75H(2)O.0.5CH(2)Cl(2) (3a), triclinic P-1, a = 14.042(2) A, b = 23.978(4) A, c = 25.195(4) A, alpha = 76.796(3) degrees, beta = 79.506(3) degrees, gamma = 77.629(3) degrees, V = 7988(2) A(3), Z = 4; Bu(4)N(2)Cu(3)(mu(3)-Cl)(2)(mu-pz)(3)Cl(3) (3b), monoclinic C2/c, a = 17.220(2) A, b = 15.606(2) A, c = 20.133(2) A, beta = 103.057(2) degrees, V = 5270(1) A(3), Z = 4; Et(3)NHCu(3)(mu(3)-OH)(mu-pz)(3)Cl(3)(pzH) (4), triclinic P-1, a = 11.498(2) A, b = 11.499(2) A, c = 12.186(2) A, alpha = 66.475(3) degrees, beta = 64.279(3) degrees, gamma = 80.183(3) degrees, V = 1331.0(5) A(3), Z = 2. Magnetic susceptibility measurements show that the three copper centers of 2 are strongly antiferromagnetically coupled with J(Cu-Cu) = -500 cm(-1).
To assess the perceptions, practices, and needs of state and local health officers with respect to professional interactions with the media.
A survey of 759 public health officers (56 state and 703 ...local) on jurisdiction demographics, frequency of media interactions, agency process for media contacts, provision and need for media training, and character of media relations.
Fifty-two state health officers and 568 US local health officers responded, for a survey response rate of 82%.
Media reporting was perceived as accurate 52% to 73% of the time, although reporters were seen as needing improved technical and scientific knowledge. Media were used frequently as a component of health education. State health jurisdictions were more likely than local jurisdictions to have a media protocol and designated media contact, to internally review media releases, to interact regularly with media, and to provide staff training on media relations. Media interaction time comprised print media (63%), television (19%), and ratio (17%). One third of the health officers found media relations adversarial, but most held a positive overall view of the media. Favorable evaluation of the media was associated with high frequency of media contact, high perceived accuracy of reporting, and presence of an institutional media protocol.
While health officers evaluated media favorably, problem areas were identified where mutual education could improve the accuracy and value of media reporting on health issues. Training capacity for both professions should be developed to increase the effectiveness of public health in media relations.
Context. Using asteroseismic techniques, it has recently become possible to probe the internal rotation profile of low-mass (~1.1-1.5 Msun) subgiant and red giant stars. Under the assumption of local ...angular momentum conservation, the core contraction and envelope expansion occurring at the end of the main sequence would result in a much larger internal differential rotation than observed. This suggests that angular momentum redistribution must be taking place in the interior of these stars. Aims. We investigate the physical nature of the angular momentum redistribution mechanisms operating in stellar interiors by constraining the efficiency of post-main sequence rotational coupling. Methods. We model the rotational evolution of a 1.25 Msun star using the Yale Rotational stellar Evolution Code. Our models take into account the magnetic wind braking occurring at the surface of the star and the angular momentum transport in the interior, with an efficiency dependent on the degree of internal differential rotation. Results. We find that models including a dependence of the angular momentum transport efficiency on the radial rotational shear reproduce very well the observations. The best fit of the data is obtained with an angular momentum transport coefficient scaling with the ratio of the rotation rate of the radiative interior over that of the convective envelope of the star as a power law of exponent ~3. This scaling is consistent with the predictions of recent numerical simulations of the Azimuthal Magneto-Rotational Instability. Conclusions. We show that an angular momentum transport process whose efficiency varies during the stellar evolution through a dependence on the level of internal differential rotation is required to explain the observed post-main sequence rotational evolution of low-mass stars.
We consider axially periodic Taylor-Couette geometry with insulating boundary conditions. The imposed basic states are so-called Chandrasekhar states, where the azimuthal flow \(U_\phi\) and magnetic ...field \(B_\phi\) have the same radial profiles. Mainly three particular profiles are considered: the Rayleigh limit, quasi-Keplerian, and solid-body rotation. In each case we begin by computing linear instability curves and their dependence on the magnetic Prandtl number Pm. For the azimuthal wavenumber m=1 modes, the instability curves always scale with the Reynolds number and the Hartmann number. For sufficiently small Pm these modes therefore only become unstable for magnetic Mach numbers less than unity, and are thus not relevant for most astrophysical applications. However, modes with m>10 can behave very differently. For sufficiently flat profiles, they scale with the magnetic Reynolds number and the Lundquist number, thereby allowing instability also for the large magnetic Mach numbers of astrophysical objects. We further compute fully nonlinear, three-dimensional equilibration of these instabilities, and investigate how the energy is distributed among the azimuthal (m) and axial (k) wavenumbers. In comparison spectra become steeper for large m, reflecting the smoothing action of shear. On the other hand kinetic and magnetic energy spectra exhibit similar behavior: if several azimuthal modes are already linearly unstable they are relatively flat, but for the rigidly rotating case where m=1 is the only unstable mode they are so steep that neither Kolmogorov nor Iroshnikov-Kraichnan spectra fit the results. The total magnetic energy exceeds the kinetic energy only for large magnetic Reynolds numbers Rm>100.
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