3,753 research outputs found
Post-transcriptional regulation of the steady-state levels of mitochondrial tRNAs in HeLa cells
In human mitochondrial DNA (mtDNA), the tRNA genes are located in three different transcription units that are transcribed at three different rates. To analyze the regulation of tRNA formation by the three transcription units, we have examined the steady-state levels and metabolic properties of the tRNAs of HeLa cell mitochondria. DNA excess hybridization experiments utilizing separated strands of mtDNA and purified tRNA samples from exponential cells long term labeled with [32P]orthophosphate have revealed a steady-state level of 6 x 10(5) tRNA molecules/cell, with three-fourths being encoded in the H-strand and one-fourth in the L-strand. Hybridization of the tRNAs with a panel of M13 clones of human mtDNA containing, in most cases, single tRNA genes and a quantitation of two-dimensional electrophoretic fractionations of the tRNAs have shown that the steady-state levels of tRNA(Phe) and tRNA(Val) are two to three times higher than the average level of the other H-strand-encoded tRNAs and three to four times higher than the average level of the L-strand-encoded tRNAs. Similar experiments carried out with tRNAs isolated from cells labeled with very short pulses of [5-3H]uridine have indicated that the rates of formation of the individual tRNA species are proportional to their steady-state amounts. Therefore, the approximately 25-fold higher rate of transcription of the tRNA(Phe) and tRNA(Val) genes relative to the other H-strand tRNA genes and the 10-16-fold higher rate of transcription of the L-strand tRNA genes relative to the H-strand tRNA genes are not reflected in the steady-state levels or the rates of formation of the corresponding tRNAs. A comparison of the steady-state levels of the individual tRNAs with the corresponding codon usage for protein synthesis, as determined from the DNA sequence and the rates of synthesis of the various polypeptides, has not revealed any significant correlation between the two parameters
Revisiting the 20th century: tales of wonder and desperation
A collection of short fiction by Michael Pearson King
Military service and crime: new evidence
BACKGROUND: Evidence indicates that a substantial proportion of military personnel are involved in high-risk and antisocial behaviors that place them at jeopardy for criminal justice system involvement. However, prior research on military service and crime has disproportionately focused on veterans from the Vietnam War era (1955–1975), and has tended to focus on either current or former military members.
METHODS: This study employed data from a population-based study (i.e., National Study on Drug Use and Health [NSDUH] between 2002 and 2014). It systematically examines the prevalence of self-reported antisocial behaviors, criminal justice system involvement, and substance abuse among the US civilian population and military service members, including reservists (n = 2206) and those who reported having been separated or retired from military service (n = 20,551). These factors are further examined across the developmental spectrum of adulthood (ages 18–34, 35–49, and 50–64).
RESULTS: Results showed that military members were more prone to lifetime arrests and overall substance misuse. However, additional findings emerged suggesting that, while the military population overall seems to be positively associated with higher criminal activity than that found in the civilian population, these findings were based on a specific subgroup of the veteran population. This subgroup is comprised of individuals who likely did not fit in with the military culture and were discharged from the military early in their careers.
CONCLUSION: Additional research on identifying this subgroup of military members is encouraged to better concentrate on prevention and treatment measures
A combined NMR and DFT study of Narrow Gap Semiconductors: The case of PbTe
In this study we present an alternative approach to separating contributions
to the NMR shift originating from the Knight shift and chemical shielding by a
combination of experimental solid-state NMR results and ab initio calculations.
The chemical and Knight shifts are normally distinguished through detailed
studies of the resonance frequency as function of temperature and carrier
concentration, followed by extrapolation of the shift to zero carrier
concentration. This approach is time-consuming and requires studies of multiple
samples. Here, we analyzed Pb and Te NMR spin-lattice
relaxation rates and NMR shifts for bulk and nanoscale PbTe. The shifts are
compared with calculations of the Pb and Te chemical shift
resonances to determine the chemical shift at zero charge carrier
concentration. The results are in good agreement with literature values from
carrier concentration-dependent studies. The measurements are also compared to
literature reports of the Pb and Te Knight shifts of - and
-type PbTe semiconductors. The literature data have been converted to the
currently accepted shift scale. We also provide possible evidence for the
"self-cleaning effect" property of PbTe nanocrystals whereby defects are
removed from the core of the particles, while preserving the crystal structure.Comment: 34 pages, 9 figure
The Fundamental Plane of Black Hole Accretion and its Use as a Black Hole-Mass Estimator
We present an analysis of the fundamental plane of black hole accretion, an
empirical correlation of the mass of a black hole (), its 5 GHz radio
continuum luminosity (), and its 2-10 keV X-ray power-law
continuum luminosity (). We compile a sample of black holes with primary,
direct black hole-mass measurements that also have sensitive,
high-spatial-resolution radio and X-ray data. Taking into account a number of
systematic sources of uncertainty and their correlations with the measurements,
we use Markov chain Monte Carlo methods to fit a mass-predictor function of the
form . Our best-fit results are , , and
with the natural logarithm of the Gaussian intrinsic scatter in the log-mass
direction . This result is a
significant improvement over our earlier mass scaling result because of the
increase in active galactic nuclei sample size (from 18 to 30), improvement in
our X-ray binary sample selection, better identification of Seyferts, and
improvements in our analysis that takes into account systematic uncertainties
and correlated uncertainties. Because of these significant improvements, we are
able to consider potential influences on our sample by including all sources
with compact radio and X-ray emission but ultimately conclude that the
fundamental plane can empirically describe all such sources. We end with advice
for how to use this as a tool for estimating black hole masses.Comment: ApJ Accepted. Online interactive version of Figure 7 available at
http://kayhan.astro.lsa.umich.edu/supplementary_material/fp
DetectiV: visualization, normalization and significance testing for pathogen-detection microarray data
DetectiV is a tool for analyzing pathogen-detection microarray datasets that allows simple visualisation, normalisation and significance testing
The White Dwarf Cooling Sequence of NGC6397
We present the results of a deep Hubble Space Telescope (HST) exposure of the
nearby globular cluster NGC6397, focussing attention on the cluster's white
dwarf cooling sequence. This sequence is shown to extend over 5 magnitudes in
depth, with an apparent cutoff at magnitude F814W=27.6. We demonstrate, using
both artificial star tests and the detectability of background galaxies at
fainter magnitudes, that the cutoff is real and represents the truncation of
the white dwarf luminosity function in this cluster. We perform a detailed
comparison between cooling models and the observed distribution of white dwarfs
in colour and magnitude, taking into account uncertainties in distance,
extinction, white dwarf mass, progenitor lifetimes, binarity and cooling model
uncertainties. After marginalising over these variables, we obtain values for
the cluster distance modulus and age of \mu_0 = 12.02 \pm 0.06 and T_c = 11.47
\pm 0.47Gyr (95% confidence limits). Our inferred distance and white dwarf
initial-final mass relations are in good agreement with other independent
determinations, and the cluster age is consistent with, but more precise than,
prior determinations made using the main sequence turnoff method. In
particular, within the context of the currently accepted \Lambda CDM
cosmological model, this age places the formation of NGC6397 at a redshift z=3,
at a time when the cosmological star formation rate was approaching its peak.Comment: 56 pages, 30 figure
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