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ABSTRACTThe expression of a gene is a tightly regulated process and is exerted by a myriad of different mechanisms. Recently, RNA modifications located in coding sequences of mRNAs, have been identified as potential regulators of gene expression. N6-methyladenosine (m6A), 5-methylcytosine (m5C), pseudouridine (Ψ) and N1-methyladenosine (m1A) have been found within open reading frames of mRNAs. The presence of these mRNA modifications has been implicated to modulate the fate of an mRNA, ranging from maturation to its translation and even degradation. However, many aspects concerning the biological functions of mRNA modifications remain elusive. Recently, systematic in vitrostudies allowed a first glimpse of the direct interplay of mRNA modifications and the efficiency and fidelity of ribosomal translation. It thereby became evident that the effects of mRNA modifications were, astonishingly versatile, depending on the type, position or sequence context. The incorporation of a single modification could either prematurely terminate protein synthesis, reduce the peptide yield or alter the amino acid sequence identity. These results implicate that mRNA modifications are a powerful mechanism to post-transcriptionally regulate gene expression.

We present a radio continuum survey of M 31 at λ6.2 cm with high sensitivity in total power and polarization, observed with the 100-m Effelsberg dish with an angular resolution of 2$\farcm$4. (1)Combination with the VLA + Effelsberg map at λ20.5 cm in total power yielded a spectral index map at $3\arcmin$resolution. Both the spectrum of the integrated emission and the spectral index distribution across M 31 indicate a nonthermal spectral index $\alpha_{{\rm n}} = 1.0\pm 0.2$. We derived maps of thermal and nonthermal emission at λ6.2 cm. Radial profiles of the various emission components north and south of the minor axis revealed that the stronger total emission in the northern part of M 31 is entirely due to stronger thermal emission, whereas the profiles of nonthermal and polarized emission are nearly identical on either side of the minor axis. This suggests that recent star formation does not lead to a local increase of the number of relativistic electrons and/or magnetic field strength. (2)We discuss several properties of the polarized emission from M 31 and their implications for the magnetic field. At λ6.2 cm the polarized intensity systematically varies along the bright “ring” of emission which shows that the regular magnetic field, $B_{{\rm reg}}$, is nearly aligned with the spiral arms forming this “ring”. The variation of the rotation measures between λ11.1 cm and λ6.2 cm, RM(11, 6), across the galaxy confirms this alignment. The nonthermal degree of polarization reaches values > $50\%$near the polarization maxima, implying that the magnetic field in M 31 is exceptionally regular.(3)We derived the distribution of the nonthermal depolarization between λ11.1 cm and λ6.2 cm, $DP_{{\rm n}}(11,6)$, which is a measure of Faraday depolarization. Gradients in RM(11, 6) may be an important cause of Faraday depolarization in M 31. The lack of anticorrelation between the thermal emission, which comes mainly from dense $\ion{H}{ii}$regions with small filling factors, and RM(11, 6) and $DP_{{\rm n}}(11,6)$indicates that rotation measures and Faraday depolarization originate in the extended diffuse ionized gas.

We present a survey of the total and linearly polarized radio continuum emission of the Andromeda galaxy at 20 cm wavelength with the VLA-D array. 7 fields were observed with 45$\prime\prime$angular resolution. The missing large-scale total emission observed with the Effelsberg telescope was inserted. This survey is the most sensitive radio continuum survey of M 31 so far and the first one in linear polarization with the VLA. The total emission of M 31 comes from extended regions and point sources. Both components are concentrated in the bright "ring” of maximum star formation at about 10 kpc radius. Nearly half of the extended emission emerges from numerous filamentary features which are typically a few arcminutes long ($\simeq 600$pc). In the field of M 31, 36 linearly polarized background sources were detected. The smallest degrees of polarization occur on the centre of the "ring” where the total emission is highest, hence on the spiral arms as delineated by Hαemission and OB associations. The distribution of polarization angles reveals coherent features of typically 1 kpc in extent, some of which show a relation to an OB association.

AbstractDeerite, a typical mineral of Fe-rich metacherts metamorphosed under blueschist conditions, is not rare, but known occurrences have up to now been restricted mainly to the Tethyan collisional zone and the Western Cordillera of North America. We describe a first occurrence in the high-pressure nappes of the Escambray Massif, Cuba, in the assemblage deerite + Mg-Al-poor riebeckite + magnetite + quartz ± garnet ± phengite ± aegirine. This assemblage typically forms during exhumation and accompanies late, stress-free annealing of the quartz matrix. Mg-Al-poor riebeckite overgrows older, large, oriented crystals of glaucophane, ferroglaucophane and Mg-Al-rich riebeckite (‘crossite’) during deerite formation. Early-formed hematite was largely replaced by magnetite. Deerite is very close to ideal composition, attaining >99% Si12O40(OH)5, allowing direct application of the experimentally determined P-T-fO2stability field (Lattard and Le Breton, 1994). In combination with oxygen-isotope thermometry on magnetite-quartz, the crystallization conditions of the deerite-bearing assemblage can be constrained to ~470°C, >15 kbar, and an oxygen fugacity restricted closely to the quartz-fayalite-magnetite buffer (fO2˜ 10-23bar). Thus, the late-stage P-Tpath ofthe metacherts mirrors a steep P-Tgradient of 10°C/km or less, requiring subduction ofthis part ofthe Antillean Island Arc to be still active during exhumation of the Escambray nappes.

The Permian siliclastic Kupferschiefer of Poland is the host for economically important CuAg deposits. Within the Kupferschiefer of the Polish Zechstein basin, mineralogical and detailed stable isotopic analyses of clay minerals, quartz and calcite show that the metal enrichment processes are associated with significant changes in oxygen and hydrogen isotope composition of the illitic clays, with a decrease in illite crystallinity and an increase in the percentages of neoformed illite (1M/1Md polytypes) in the clay size fractions. D/H and 18O/16O ratios of the minerals in the host rock have been affected by the mineralizing process. The magnitude of the isotopic shift in 18O/16O (δ18O of illite decreases of ∼4‰) and D/H of illitic clays (δD increases of ∼40‰) corresponds with distance to “Rote Fäule” and Cu-mineralized zones within the Kupferschiefer. The isotopic zonation of fine-grained illite is explained by fluid-rock interaction with ascending, oxidizing solutions, which are thought to have been responsible for base metal deposition and formation of Rote Fäule. Published microthermometric fluid inclusion data and the degree of maturation of organic matter imply a maximum temperature between 100° and 150°C during host rock alteration and ore formation. The characterization of the fluids as basinal brines were confirmed by the published fluid inclusion studies. The estimated isotopic composition of the mineralizing brines (δ18O between +2 and +7‰; δD between −3 and −23‰) argue for its origin from meteoric waters by salt dissolution and evaporation in the sedimentary basin of the Rotliegendes. A participation of heated geopressured brines from Zechstein salt-bearing rocks and, therefore, an origin from evaporated seawater cannot be excluded. The results, together with previously published KAr data on illite, argue for a post-depositional origin of base metal mineralization within the Kupferschiefer of Poland. The metals were most probably derived by leaching of Rotliegendes volcanics with the saline waters. Upward migration and penetration into the Kupferschiefer were restricted to zones of enhanced permeability at the margins of the sedimentary basin and adjacent to paleohighs.