Human and bacterial DNA polymerases discriminate against 8-oxo-2'-deoxyadenosine- 5'-triphosphate

Цель. 8-оксоаденин – распространенное поврежденное основание, ассоциированное с онкологическими и нейродегенеративными заболеваниями. Оно может возникать вследствие непосредственного окисления аденина в ДНК или при включении окисленного dNTP. Методы. Разработан эффективный способ синтеза 8-оксо-2'-дезоксиаденозин-5'-трифосфата и изучено его включение в ДНК разными ДНК-полимеразами. Результаты. Фрагмент Кленова ДНК-полимеразы I с невысокой эффективностью включал oA напротив гуанина. Для ДНК-полимеразы наблюдалось ограниченное включение oA напротив гуанина и аденина, а для ДНК-полимеразы b – напротив аденина, тимина и гуанина. Выводы. Как источник oA в геноме окисление аденина в ДНК может иметь большее значение, чем окисление dATP. Kлючевые слова: мутагенез, повреждение ДНК, оксидативный стресс, 8-оксоаденин, ДНК полимеразы.Мета. 8-оксоаденін – розповсюджена пошкоджена основа, асо- ційована з онкологічними і нейродегенеративними захворюваннями. Воно може виникати внаслідок безпосереднього окиснення аденіну в ДНК або при вбудовуванні окисненого dNTP. Методи. Розроблено ефективний спосіб синтезу 8-оксо-2'-дезоксиаденозин-5'-трифосфату і вивчено його включення в ДНК різними ДНК- полімеразами. Результати. Фрагмент Кленова ДНК-полі- мерази I з невисокою ефективністю включав oA навпроти гуаніну. Для ДНК-полімерази спостерігалося обмежене включення oA навпроти гуаніну і аденіну, а для ДНК-полімерази b – навпроти аденіну, тиміну і гуаніну. Висновки. Як джерело oA в геномі окиснення аденіну в ДНК може мати більше значення, ніж окиснення dATP. Ключові слова: мутагенез, пошкодження ДНК, оксидативний стрес, 8-оксоаденін, ДНК-полімерази.Aim. 8-Oxoadenine is an abundant DNA lesion associated with cancer and neurodegeneration. It may appear through direct oxidation of adenine in DNA or by incorporation from the oxidized dNTP pool. Methods. We developed an efficient method of synthesizing 8-oxo-2'-deoxyadenosine-5'-triphosphate and studied its incorporation by various DNA polymerases. Results. oA was weakly misincorporated opposite guanine by the DNA polymerase I Klenow fragment. Limited incorporation of oA was observed opposite guanine and adenine with DNA polymerase a, and opposite adenine, thymine and guanine with DNA polymerase b. Conclusions. Adenine oxidation in DNA may outweigh damage to dATP as a source of genomic oA. Keywords: mutagenesis, DNA damage, oxidative stress, 8-oxoadenine, DNA polymerases

Time-distance analysis of the emerging active region NOAA 10790

We investigate the emergence of Active Region NOAA 10790 by means of time – distance helioseismology. Shallow regions of increased sound speed at the location of increased magnetic activity are observed, with regions becoming deeper at the locations of sunspot pores. We also see a long-lasting region of decreased sound speed located underneath the region of the flux emergence, possibly relating to a temperature perturbation due to magnetic quenching of eddy diffusivity, or to a dense flux tube. We detect and track an object in the subsurface layers of the Sun characterised by increased sound speed which could be related to emerging magnetic-flux and thus obtain a provisional estimate of the speed of emergence of around 1 km s−1

Bodily tides near spin-orbit resonances

Spin-orbit coupling can be described in two approaches. The method known as "the MacDonald torque" is often combined with an assumption that the quality factor Q is frequency-independent. This makes the method inconsistent, because the MacDonald theory tacitly fixes the rheology by making Q scale as the inverse tidal frequency. Spin-orbit coupling can be treated also in an approach called "the Darwin torque". While this theory is general enough to accommodate an arbitrary frequency-dependence of Q, this advantage has not yet been exploited in the literature, where Q is assumed constant or is set to scale as inverse tidal frequency, the latter assertion making the Darwin torque equivalent to a corrected version of the MacDonald torque. However neither a constant nor an inverse-frequency Q reflect the properties of realistic mantles and crusts, because the actual frequency-dependence is more complex. Hence the necessity to enrich the theory of spin-orbit interaction with the right frequency-dependence. We accomplish this programme for the Darwin-torque-based model near resonances. We derive the frequency-dependence of the tidal torque from the first principles, i.e., from the expression for the mantle's compliance in the time domain. We also explain that the tidal torque includes not only the secular part, but also an oscillating part. We demonstrate that the lmpq term of the Darwin-Kaula expansion for the tidal torque smoothly goes through zero, when the secondary traverses the lmpq resonance (e.g., the principal tidal torque smoothly goes through nil as the secondary crosses the synchronous orbit). We also offer a possible explanation for the unexpected frequency-dependence of the tidal dissipation rate in the Moon, discovered by LLR

On the Detectability and Use of Normal Modes for Determining Interior Structure of Mars

The InSight mission to Mars is well underway and will be the first mission to acquire seismic data from a planet other than Earth. In order to maximise the science return of the InSight data, a multifaceted approach will be needed that seeks to investigate the seismic data from a series of different frequency windows, including body waves, surface waves, and normal modes. Here, we present a methodology based on globally-averaged models that employs the long-period information encoded in the seismic data by looking for fundamental-mode spheroidal oscillations. From a preliminary analysis of the expected signal-to-noise ratio, we find that normal modes should be detectable during nighttime in the frequency range 5–15 mHz. For improved picking of (fundamental) normal modes, we show first that those are equally spaced between 5–15 mHz and then show how this spectral spacing, obtained through autocorrelation of the Fourier-transformed time series can be further employed to select normal mode peaks more consistently. Based on this set of normal-mode spectral frequencies, we proceed to show how this data set can be inverted for globally-averaged models of interior structure (to a depth of ∼250 km), while simultaneously using the resultant synthetically-approximated normal mode peaks to verify the initial peak selection. This procedure can be applied iteratively to produce a “cleaned-up” set of spectral peaks that are ultimately inverted for a “final” interior-structure model. To investigate the effect of three-dimensional (3D) structure on normal mode spectra, we constructed a 3D model of Mars that includes variations in surface and Moho topography and lateral variations in mantle structure and employed this model to compute full 3D waveforms. The resultant time series are converted to spectra and the inter-station variation hereof is compared to the variation in spectra computed using different 1D models. The comparison shows that 3D effects are less significant than the variation incurred by the difference in radial models, which suggests that our 1D approach represents an adequate approximation of the global average structure of Mars

The seismic OPTIMISM experiment

International audienceThe study of the deep interior of Mars suffers from the very limited amount of data available, particularly seismological data. The objective of the OPTIMISM seismic experiment, lost with the failure of the Mars 96 mission, was to perform a seismic reconnaissance of Mars, to constrain the level of martian seismic noise and its level of seismicity. The seismometer was expected to operate during one year, with a sensitivity one hundred times higher than the Viking seismometer.Observation of relatively frequent low magnitude marsquakes, as well as a few large magnitude quakes might then be probably achieved. The OPTIMISM experiment might then, as a seismic ‘path-finder’, open a new field in Mars exploration and a new era in our present knowledge of the interior of Mars. A seismic experiment on Mars, especially performed by a network of stations, remains as the necessary experiment for the determination of the internal structure of the planet

The seismic OPTIMISM experiment

International audienceThe study of the deep interior of Mars suffers from the very limited amount of data available, particularly seismological data. The objective of the OPTIMISM seismic experiment, lost with the failure of the Mars 96 mission, was to perform a seismic reconnaissance of Mars, to constrain the level of martian seismic noise and its level of seismicity. The seismometer was expected to operate during one year, with a sensitivity one hundred times higher than the Viking seismometer.Observation of relatively frequent low magnitude marsquakes, as well as a few large magnitude quakes might then be probably achieved. The OPTIMISM experiment might then, as a seismic ‘path-finder’, open a new field in Mars exploration and a new era in our present knowledge of the interior of Mars. A seismic experiment on Mars, especially performed by a network of stations, remains as the necessary experiment for the determination of the internal structure of the planet