3,622 research outputs found
Roles of transcriptional and translational control mechanisms in regulation of ribosomal protein synthesis in Escherichia coli
ABSTRACTBacterial ribosome biogenesis is tightly regulated to match nutritional conditions and to prevent formation of defective ribosomal particles. InEscherichia coli, most ribosomal protein (r-protein) synthesis is coordinated with rRNA synthesis by a translational feedback mechanism: when r-proteins exceed rRNAs, specific r-proteins bind to their own mRNAs and inhibit expression of the operon. It was recently discovered that the second messenger nucleotide guanosine tetra and pentaphosphate (ppGpp), which directly regulates rRNA promoters, is also capable of regulating many r-protein promoters. To examine the relative contributions of the translational and transcriptional control mechanisms to the regulation of r-protein synthesis, we devised a reporter system that enabled us to genetically separate thecis-acting sequences responsible for the two mechanisms and to quantify their relative contributions to regulation under the same conditions. We show that the synthesis of r-proteins from the S20 and S10 operons is regulated by ppGpp following shifts in nutritional conditions, but most of the effect of ppGpp required the 5′ region of the r-protein mRNA containing the target site for translational feedback regulation and not the promoter. These results suggest that most regulation of the S20 and S10 operons by ppGpp following nutritional shifts is indirect and occurs in response to changes in rRNA synthesis. In contrast, we found that the promoters for the S20 operon were regulated during outgrowth, likely in response to increasing nucleoside triphosphate (NTP) levels. Thus, r-protein synthesis is dynamic, with different mechanisms acting at different times.IMPORTANCEBacterial cells have evolved complex and seemingly redundant strategies to regulate many high-energy-consuming processes. InE. coli, synthesis of ribosomal components is tightly regulated with respect to nutritional conditions by mechanisms that act at both the transcription and translation steps. In this work, we conclude that NTP and ppGpp concentrations can regulate synthesis of ribosomal proteins, but most of the effect of ppGpp is indirect as a consequence of translational feedback in response to changes in rRNA levels. Our results illustrate how effects of seemingly redundant regulatory mechanisms can be separated in time and that even when multiple mechanisms act concurrently their contributions are not necessarily equivalent.</jats:p
Ecological analysis of world trade
Ecological systems have a high level of complexity combined with stability
and rich biodiversity. Recently, the analysis of their properties and evolution
has been pushed forward on a basis of concept of mutualistic networks that
provides a detailed understanding of their features being linked to a high
nestedness of these networks. It was shown that the nestedness architecture of
mutualistic networks of plants and their pollinators minimizes competition and
increases biodiversity. Here, using the United Nations COMTRADE database for
years 1962 - 2009, we show that a similar ecological analysis gives a valuable
description of the world trade. In fact the countries and trade products are
analogous to plants and pollinators, and the whole trade network is
characterized by a low nestedness temperature which is typical for the
ecological networks. This approach provides new mutualistic features of the
world trade highlighting new significance of countries and trade products for
the world trade.Comment: 5 pages, 6 figures (6 extra figures in Supporting Information
Coordination des actions impliquees dans le reboisement forestier pour obtenir la maximum de'efficacite et d'economie d'ensembre dans les trabaux
International Union of Forest Research Organizations . World Congress 17o . 1981 . Japon)Depto. de Estadística e Investigación OperativaFac. de Ciencias MatemáticasTRUEpu
New Superhard Phases for 3D C60-based Fullerites
We have explored new possible phases of 3D C60-based fullerites using
semiempirical potentials and ab-initio density functional methods. We have
found three closely related structures - two body centered orthorhombic and one
body centered cubic - having 52, 56 and 60 tetracoordinated atoms per molecule.
These 3D polymers result in semiconductors with bulk moduli near 300 GPa, and
shear moduli around 240 GPa, which make them good candidates for new low
density superhard materials.Comment: To be published in Physical Review Letter
Photocontrol of productivity and stem elongation of three Rosa x hybrida L. cultivars under photoselective films
Se evaluaron los cambios en la radiación
transmitida a través de films fotoselectivos (FS)
fluorescentes y el impacto de estos cambios sobre
la producción de tres cultivares de rosa para corte
Fuego Negro, Maroussia y Anna. Se observó que
los FS nuevos o expuestos a la radiación solar
vs. noFS disminuyen la transmisión de radiación
azul (A) (-28,4 a -32,9%, respectivamente),
incrementan el R produciendo una relación R:RL
mayor (+3,6%), si bien transmiten algo menos
de radiación fotosintéticamente activa que los
noFS nuevos. El número de rosas producidas
fue significativamente mayor bajo el FS vs. noFS
en los tres cv (+24, +32 y +36% en Anna, Fuego
Negro y Maroussia, respectivamente), con un peso
fresco y seco (PF y PS) significativamente mayor
y tallos florales más largos en Anna y Maroussia
(50,69 y 43,91 cm vs. 38,91 y 40,04 cm en
invierno y primavera, respectivamente), y
pimpollos significativamente más largos y de
mayor PF y PS en los tres cv. Mayor relación
R:RL y menor UV-A y A en la radiación transmitida
por films FS aumentaron la cantidad y calidad
de determinados cultivares de rosas mostrando
una alternativa a los reguladores químicos
de crecimiento.This research evaluate changes in the
radiation transmitted through a photoselective,
fluorescent polyethylene film (PS), and the
impact of these changes on the production of
three cut rose cultivars, Fuego Negro, Maroussia
and Anna. PS vs. nonPS films, new or exposed
to solar radiation, decreased transmission of blue
radiation (-28.4 to -32.9%, PS-new and PS-old,
respectively), increased red radiation, resulting
in a R:FR ratio greater 3.6% than for nonPS,
although, PS-new and PS-old films transmitted
a smaller percentage of PAR than non-PS-new
(-16.6 and -22.4%, respectively). The number of
roses harvested was significantly higher under
PS vs. nonPS film for the three cultivars (+24,
+32 and +36% flowers m-2, in Anna, Fuego Negro
and Maroussia, respectively), with significantly
higher fresh weight (FW) and dry weight (DW),
longer floral stems in Anna and Maroussia (50.69
and 43.91 cm vs. 38.91 and 40.04 in winter
and spring, respectively) and buds significantly
longer and higher FW and DW in the three cv.
Higher R:FR and lower UV-A and B radiation of
PS greenhouse covers increased quantity and
quality of some of these rose cultivars featuring
an alternative to chemical growth regulators.Fil: Mascarini, Libertad.
Universidad de Buenos Aires. Facultad de AgronomíaFil: Lorenzo, Gabriel A..
Universidad de Buenos Aires. Facultad de AgronomíaFil: Burgos, Marcelo L..
Universidad de Buenos Aires. Facultad de Agronomí
Sox9 and Sox8 protect the adult testis from male-to-female genetic reprogramming and complete degeneration.
The new concept of mammalian sex maintenance establishes that particular key genes must remain active in the differentiated gonads to avoid genetic sex reprogramming, as described in adult ovaries after Foxl2 ablation. Dmrt1 plays a similar role in postnatal testes, but the mechanism of adult testis maintenance remains mostly unknown. Sox9 and Sox8 are required for postnatal male fertility, but their role in the adult testis has not been investigated. Here we show that after ablation of Sox9 in Sertoli cells of adult, fertile Sox8(-/-) mice, testis-to-ovary genetic reprogramming occurs and Sertoli cells transdifferentiate into granulosa-like cells. The process of testis regression culminates in complete degeneration of the seminiferous tubules, which become acellular, empty spaces among the extant Leydig cells. DMRT1 protein only remains in non-mutant cells, showing that SOX9/8 maintain Dmrt1 expression in the adult testis. Also, Sox9/8 warrant testis integrity by controlling the expression of structural proteins and protecting Sertoli cells from early apoptosis. Concluding, this study shows that, in addition to its crucial role in testis development, Sox9, together with Sox8 and coordinately with Dmrt1, also controls adult testis maintenance
Synthesis of Positron Emission Tomography (PET) Images via Multi-channel Generative Adversarial Networks (GANs)
Positron emission tomography (PET) image synthesis plays an important role,
which can be used to boost the training data for computer aided diagnosis
systems. However, existing image synthesis methods have problems in
synthesizing the low resolution PET images. To address these limitations, we
propose multi-channel generative adversarial networks (M-GAN) based PET image
synthesis method. Different to the existing methods which rely on using
low-level features, the proposed M-GAN is capable to represent the features in
a high-level of semantic based on the adversarial learning concept. In
addition, M-GAN enables to take the input from the annotation (label) to
synthesize the high uptake regions e.g., tumors and from the computed
tomography (CT) images to constrain the appearance consistency and output the
synthetic PET images directly. Our results on 50 lung cancer PET-CT studies
indicate that our method was much closer to the real PET images when compared
with the existing methods.Comment: 9 pages, 2 figure
Cell adhesion on ti surface with controlled roughness
In this report, the in situ interaction between Saos-2 osteoblast cells and a smooth Ti surface was examined over time. The adhesion kinetics and mechanisms of cellular proliferation were monitored by quartz crystal microbalance (QCM) and electrochemical impedance spectroscopy (EIS). The rate of Saos-2 attachment on Ti surfaces, obtained from the measurements performed with the QCM, is a first-order reaction, with k=2.103 min1. The impedance measurements indicate that in the absence of cells, the Ti resistance diminishes over time (7 days), due to the presence of amino acids and proteins from the culture medium that have been a dsorbed, while in the presence of osteoblasts, this decrease is much greater because of the compounds generated by the cells that accelerate the dissolution of TiAdhesión de osteoblastos sobre una superficie de Ti de rugosidad controlada. En este trabajo, se ha estudiado la interacción in situ entre células osteoblásticas Saos-2 y una superficie de Ti de rugosidad controlada a lo largo del tiempo. El estudio de la cinética y los mecanismos de proliferación celular de adhesión se ha realizado a través de la microbalanza de cristal de cuarzo (QCM) y espectroscopía de impedancia electroquímica (EIS). La velocidad de adhesión de los osteoblastos sobre la superficie de Ti obtenida a través de medidas con la QCM, sigue una reacción de primer orden, con k=2×10−3 min−1. Los ensayos de impedancia indican que, en ausencia de las células, la resistencia del Ti disminuye con el tiempo (7 días), debido a la presencia de aminoácidosy proteínas del medio de cultivo que se han adsorbido, mientras que en presencia de células, esta disminución es mucho mayor debido a los productos metabólicos generados por las células que aceleran la disolución del TiThe authors thank the financial support under projects MAT 2008-06719-C03-01, CTQ2008-05775/ BQU and by the Comunidad Autónoma de Madrid (CAM) through AVANSENS S2009/PPQ-164
The c-completion of Lorentzian metric spaces
Inspired by some Lorentzian versions of the notion of metric and length space introduced by Kunzinger and Sämman [24], and more recently, by Müller [31], and Minguzzi and Sühr [30], we revisit the notion of Lorentzian metric space in order to later construct the c-completion of these general objects. We not only prove that this construction is feasible in great generality for these objects, including spacetimes of low regularity, but also endow the c-completion with a structure of Lorentzian metric space by itself. We also prove that the c-completion constitutes a well-suited extension of the original space, which really completes it in a precise sense and becomes sensible to certain causal properties of that space.Project PID2020-116126GB-I00 (funded by
MCIN/AEI/10.13039/501100011033)IMAG-María de Maeztu grant CEX2020-
001105-M (funded by MCIN/AEI/10.13039/50110001103)Grants PID2020-118452GBI00 and PID2021-126217NBI00
(Spanish MICINN)PY20-01391 (PAIDI 2020, Junta de Andalucía-FEDER
- …