Single transcriptional and translational preQ1 riboswitches adopt similar pre-folded ensembles that follow distinct folding pathways into the same ligand-bound structure

Riboswitches are structural elements in the 50 untranslated regions of many bacterial messenger RNAs that regulate gene expression in response to changing metabolite concentrations by inhibition of either transcription or translation initiation. The preQ1 (7-aminomethyl-7-deazaguanine) riboswitch family comprises some of the smallest metabolite sensing RNAs found in nature. Once ligand-bound, the transcriptional Bacillus subtilis and translational Thermoanaerobacter tengcongensis preQ1 riboswitch aptamers are structurally similar RNA pseudoknots; yet, prior structural studies have characterized their ligand-free conformations as largely unfolded and folded, respectively. In contrast, through single molecule observation, we now show that, at nearphysiological Mg2+ concentration and pH, both ligand-free aptamers adopt similar pre-folded state ensembles that differ in their ligand-mediated folding. Structure-based Go¯ -model simulations of the two aptamers suggest that the ligand binds late (Bacillus subtilis) and early (Thermoanaerobacter tengcongensis) relative to pseudoknot folding, leading to the proposal that the principal distinction between the two riboswitches lies in their relative tendencies to fold via mechanisms of conformational selection and induced fit, respectively. These mechanistic insights are put to the test by rationally designing a single nucleotide swap distal from the ligand binding pocket that we find to predictably control the aptamers0 pre-folded states and their ligand binding affinities

Sex-specific changes in gene expression and delayed sex differentiation in response to estrogen pollution in grayling (Salmonidae)

The synthetic 17α-ethinylestradiol (EE2) is an estrogenic compound of oral contraceptives and therefore a common pollutant that has been suspected to affect the demography of river-dwelling salmonids. We study a population of European grayling (Thymallus thymallus) that suffers from sex ratio distortions. Here we test how ecologically relevant concentrations of EE2 affect sex-specific gene expression around early stages of sex differentiation. We collected gametes from F1s of wild spawners, used them for in vitro fertilizations, and raised the resulting embryos singly under experimentally controlled conditions. Embryos were either exposed to 1ng/L EE2 or sham-exposed. RNA was collected from samples taken 10 days before hatching, at the day of hatching, and towards the end of the yolk-sac stage, to study gene expression and relate it to genetic sex (sdY genotype). We found that EE2 affects gene expression of a very large number of genes especially at the day of hatching. The effects of EE2 on gene expression is strongly sex-specific. At the day of hatching, EE2 affected about twice as many genes in females than in males, and towards the end of the yolk-sac larval stage, EE2 effects were nearly exclusively observed in females. Among the many effects was, for example, a surprising EE2-induced molecular masculinization in the females’ heads. Histological examination of gonadal development of EE2-treated or sham-exposed juveniles during the first 4.5 months after hatching revealed a delaying effect of EE2 on sex differentiation. Because grayling sex determination goes through an all-male stage (a rare case of undifferentiated gonochorism), the rate of EE2-induced sex reversal could not be unequivocally determined during the observational period. However, two EE2-treated genetic males had ovarian tissues at the end of the study. We conclude that common levels of EE2 pollution affect grayling from very early stages on by interfering with male and female gene expression around the onset of sex differentiation, by delaying sex differentiation, and by feminizing some males

An introduction to genetic quality in the context of sexual selection

This special issue of Genetica brings together empirical researchers and theoreticians to present the latest on the evolutionary ecology of genetic quality in the context of sexual selection. The work comes from different fields of study including behavioral ecology, quantitative genetics and molecular genetics on a diversity of organisms using different approaches from comparative studies, mathematical modeling, field studies and laboratory experiments. The papers presented in this special issue primarily focus on genetic quality in relation to ( 1) sources of genetic variation, ( 2) polyandry, ( 3) new theoretical developments and ( 4) comprehensive reviews

Trajectory studies of Polar Statospheric Cloud Lidar Observations at Sodankyla (Finland) during SESAME: comparison with box model results of particle evolution

Polar statospheric clouds (PSC) were observed with the milti-wavelengh lidar of the MOANA project during SESAME. The physical state, liquid or solid, of the cloud particles can be inferred from the lidar data. Using isentropic back-trajectories to obtain the thermal history of the sampled air masses, it is possible to reconcile most of the observations with current ideas on PSC formation and evolution. When the cloud particles were identified as liquid, changes in the size distributionof the droplets along the trajectory ewre calculated using micro-physical box model. Backscatter ratios ......Published165-1811.8. Osservazioni di geofisica ambientaleJCR Journalreserve

Lidar observations of liquid and solid PSC at Sodankyla

Polar stratospheric clouds (PSC) play a major role in the process of Artic and Antartic ozone depletion due to the surface provided for heterogeneus chemical reactions and the removal of NO2 from the gas phase. Therefore the phase, size and composition of PSC's should be known. The microphysical structure of the PSC's depends on the actual temperature and the corresponding; airmass thermal history. At temperatures below the ice frostpoint, PSC's of ice particles (Type II) are observed, while PSC's seen at temperatures above the frostpoint are classified as PSC Type Ia (anisotropic particles) and PSC Ib (spherical particles). PSC I were believed to consist of nitric acid trihydrate (NA'r). NAT should be stable some degrees above the ice frostpoint with a particle shape depending on the cooling rate [Toon et al., 1990]. However, the explanation of PSC based solely on the NAT-hypothesis can not explain a large amount of data [Toon and Tolbert, 1995]. The spherical shape of PSC Ib can be explained with a liquid supercooled ternary solution (STS) consisting of H2O, HNO3 and H2SO4. Scenarios for the formation of frozen background aerosol (sulfuric acid tetrahydrate, SAT) are now investigated. The described variance in shape and size of the PSC can be sensed by multispectral 2-polarization lidar, measuring range resolved scattering properties of atmospheric aerosols. Here the lidar observations of PSC's during the SESAME campaign are compared to the critical formation temperatures of the different PSC types.PublishedSchliersee, Germany1.8. Osservazioni di geofisica ambientaleope

Microlayers of solid particles observed by lidar at Sodankyla during SESAME

The physical condition of polar stratospheric aerosols is of great importance both for the modelling of surface chemistry reactions and for the understanding of particle production and evaporation in the polar vortex. The particles can be either liquid, supercooled liquids or solid material at different heights and temperatures. Since a solid particle can survive much longer when temperature rises above the freezing point, whereas liquid particles will evaporate quickly at temperatures above the condensation temperature, the knowledge of the physical state is an important parameter to estimate the contribution to heterogenous chemistry of the different aerosol types observed.SubmittedSchliersee, Germany1.8. Osservazioni di geofisica ambientaleope

Cooperation under Indirect Reciprocity and Imitative Trust

Indirect reciprocity, a key concept in behavioral experiments and evolutionary game theory, provides a mechanism that allows reciprocal altruism to emerge in a population of self-regarding individuals even when repeated interactions between pairs of actors are unlikely. Recent empirical evidence show that humans typically follow complex assessment strategies involving both reciprocity and social imitation when making cooperative decisions. However, currently, we have no systematic understanding of how imitation, a mechanism that may also generate negative effects via a process of cumulative advantage, affects cooperation when repeated interactions are unlikely or information about a recipient's reputation is unavailable. Here we extend existing evolutionary models, which use an image score for reputation to track how individuals cooperate by contributing resources, by introducing a new imitative-trust score, which tracks whether actors have been the recipients of cooperation in the past. We show that imitative trust can co-exist with indirect reciprocity mechanisms up to a threshold and then cooperation reverses -revealing the elusive nature of cooperation. Moreover, we find that when information about a recipient's reputation is limited, trusting the action of third parties towards her (i.e. imitating) does favor a higher collective cooperation compared to random-trusting and share-alike mechanisms. We believe these results shed new light on the factors favoring social imitation as an adaptive mechanism in populations of cooperating social actors

Polar Stratospheric Cloud Measurements by Multispectral Lidar at Sodankyla in Winter 1994/95

Polar stratospheric clouds (PSC) play a major role in the process of Arctic and Antarctic ozone depletion due to heterogeneous chemical reactions responsible for chlorine acti-vation, and particle sedimentation redistributing nitrogen species in the stratosphere. Therefore the phase, size and the composition of PSCs should be known. PSC can be divided into PSC type I, observed at temperatures some degrees above the ice frostpoint, and PSC type II consisting of water ice particles occurring at temperatures below the frostpoint. PSC type I can be subdivided into aspherical (type Ia) and spherical (type Ib) particles. Measurements of gas phase HNO3 removal in presence of PSCs and labora¬tory studies led to the assumption that PSC type I consist of nitric acid trihydrate and theparticle shape depends on the cooling rate [1]. However the explanation ofPSC I based solely on the NAT-hypothesis can not explain a large amount of data [2], and other compositions like liquid supercooled ternary solu¬tions (STS) of H2O, HNO3 and H2SO 4 are discussed now [3]. Multiwavelength, 2-polarization lidar measurements give information about the size distribution, refractive index and physical state of the cloud particles.PublishedBerlin, Germany1.8. Osservazioni di geofisica ambientaleope