88 research outputs found
Detection of snRNP assembly intermediates in Cajal bodies by fluorescence resonance energy transfer
Spliceosomal small nuclear ribonucleoprotein particles (snRNPs) are required for pre-mRNA splicing throughout the nucleoplasm, yet snRNPs also concentrate in Cajal bodies (CBs). To address a proposed role of CBs in snRNP assembly, we have used fluorescence resonance energy transfer (FRET) microscopy to investigate the subnuclear distribution of specific snRNP intermediates. Two distinct complexes containing the protein SART3 (p110), required for U4/U6 snRNP assembly, were localized: SART3âąU6 snRNP and SART3âąU4/U6 snRNP. These complexes segregated to different nuclear compartments, with SART3âąU6 snRNPs exclusively in the nucleoplasm and SART3âąU4/U6 snRNPs preferentially in CBs. Mutant cells lacking the CB-specific protein coilin and consequently lacking CBs exhibited increased nucleoplasmic levels of SART3âąU4/U6 snRNP complexes. Reconstitution of CBs in these cells by expression of exogenous coilin restored accumulation of SART3âąU4/U6 snRNP in CBs. Thus, while some U4/U6 snRNP assembly can occur in the nucleoplasm, these data provide evidence that SART3âąU6 snRNPs form in the nucleoplasm and translocate to CBs where U4/U6 snRNP assembly occurs
Granite microporosity changes due to fracturing and alteration: secondary mineral phases as proxies for porosity and permeability estimation
Several alteration facies of fractured Lipnice granite are
studied in detail on borehole samples by means of mercury intrusion porosimetry,
polarized and fluorescent light microscopy, and microprobe chemical analyses. The goal is
to describe the granite void space geometry in the vicinity of fractures with alteration
halos and to link specific geometries with simply detectable parameters to facilitate
quick estimation of porosity and permeability based on, for example, drill cuttings. The
core of the study is the results of porosity and throat size distribution analyses on 21
specimens representing unique combinations of fracture-related structures within six
different alteration facies basically differing in secondary phyllosilicate chemistry and
porosity structure. Based on a simple model to calculate permeability from the measured
porosities and throat size distributions, the difference in permeability between the
fresh granite and the most fractured and altered granite is 5 orders of magnitude. Our
observations suggest that the porosity, the size of connections and the proportion of
crack porosity increase with fracture density, while precipitation of iron-rich infills
as well as of fine-grained secondary phyllosilicates acts in the opposite way. Different
styles and intensities of such end-member agents shape the final void space geometry and
imply various combinations of storage, transport and retardation capacity for specific
structures. This study also shows the possibility to use standard mercury intrusion
porosimetry with advanced experimental settings and data treatment to distinguish
important differences in void space geometry within a span of a few percent of porosity.</p
Problems and challenges in detection of pre-Mesozoic maar volcanoes: example from the PrincipĂĄlek Volcano in the Permian KrkonoĆĄe Piedmont Basin
Assessment of spectral UV radiation at Marambio Base, Antarctic Peninsula
This study aims to assess the dependence of spectral UV
radiation on different atmospheric and terrestrial factors, including solar
zenith angle, ozone, and cloud cover, in the southern polar environment. For
this purpose, 23â260 spectra (300â363ânm), obtained by the B199 Mk-III
Brewer spectrophotometer at Marambio Base, Antarctic Peninsula region, over
the period 2010â2020, were studied. A neural network model was developed to
investigate the effects of the explanatory variables at 127 wavelengths in
the interval 300â363ânm, with a 0.5ânm sampling interval. Solar zenith
angle (SZA) proved to be the most important parameter, followed by cloud
cover, total ozone column (TOC), and surface albedo. The relative SZA effect
is greatest at the shortest wavelengths, where a 1â decrease in
SZA results in a 6â%â18â% increase in UV irradiance (305ânm). TOC
particularly affects the short wavelengths below approximately 320â325ânm, when for
example at 305ânm a 10âDU decrease in TOC causes a 7â%â13â% increase in
UV irradiance. The large-scale ozone holes (e.g., in 2011â2012, 2014â2015,
2018â2019) caused the spectral UV irradiance at very short wavelengths to peak
in spring, whereas in other seasons (e.g., 2010â2011, 2012â2013), the
maxima at all wavelengths were recorded in summer (November to January).
Absorption of UV radiance by the ozone also affected the temporal distribution
of very high spectral UV irradiances (i.e., highest 10â% of the
distribution), when at 305ânm they were observed both in spring and summer
months, and at 340ânm they occurred mostly in summer. The effect of cloud
cover was strongest near the fully cloudy sky and in the summer months, when
the Antarctic clouds tend to be thickest.</p
Positive solutions and eigenvalue intervals of a nonlinear singular fourth-order boundary value problem
Histone Deacetylase Activity Modulates Alternative Splicing
There is increasing evidence to suggest that splicing decisions are largely made when the nascent RNA is still associated with chromatin. Here we demonstrate that activity of histone deacetylases (HDACs) influences splice site selection. Using splicing-sensitive microarrays, we identified âŒ700 genes whose splicing was altered after HDAC inhibition. We provided evidence that HDAC inhibition induced histone H4 acetylation and increased RNA Polymerase II (Pol II) processivity along an alternatively spliced element. In addition, HDAC inhibition reduced co-transcriptional association of the splicing regulator SRp40 with the target fibronectin exon. We further showed that the depletion of HDAC1 had similar effect on fibronectin alternative splicing as global HDAC inhibition. Importantly, this effect was reversed upon expression of mouse HDAC1 but not a catalytically inactive mutant. These results provide a molecular insight into a complex modulation of splicing by HDACs and chromatin modifications
The differential interaction of snRNPs with pre-mRNA reveals splicing kinetics in living cells
GFP-tagged snRNP components reveal the dynamics and rate for spliceosome assembly in vivo
Fractional order differential equations with iterations of linear modification of the argument
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