Applications of electrified dust and dust devil electrodynamics to Martian atmospheric electricity

Atmospheric transport and suspension of dust frequently brings electrification, which may be substantial. Electric fields of 10 kVm-1 to 100 kVm-1 have been observed at the surface beneath suspended dust in the terrestrial atmosphere, and some electrification has been observed to persist in dust at levels to 5 km, as well as in volcanic plumes. The interaction between individual particles which causes the electrification is incompletely understood, and multiple processes are thought to be acting. A variation in particle charge with particle size, and the effect of gravitational separation explains to, some extent, the charge structures observed in terrestrial dust storms. More extensive flow-based modelling demonstrates that bulk electric fields in excess of 10 kV m-1 can be obtained rapidly (in less than 10 s) from rotating dust systems (dust devils) and that terrestrial breakdown fields can be obtained. Modelled profiles of electrical conductivity in the Martian atmosphere suggest the possibility of dust electrification, and dust devils have been suggested as a mechanism of charge separation able to maintain current flow between one region of the atmosphere and another, through a global circuit. Fundamental new understanding of Martian atmospheric electricity will result from the ExoMars mission, which carries the DREAMS (Dust characterization, Risk Assessment, and Environment Analyser on the Martian Surface)-MicroARES (Atmospheric Radiation and Electricity Sensor) instrumentation to Mars in 2016 for the first in situ measurements

Evidence that Errors Made by DNA Polymerase α are Corrected by DNA Polymerase δ

SummaryEukaryotic replication [1, 2] begins at origins and on the lagging strand with RNA-primed DNA synthesis of a few nucleotides by polymerase α, which lacks proofreading activity. A polymerase switch then allows chain elongation by proofreading-proficient pol δ and pol ɛ. Pol δ and pol ɛ are essential, but their roles in replication are not yet completely defined [3]. Here, we investigate their roles by using yeast pol α with a Leu868Met substitution [4]. L868M pol α copies DNA in vitro with normal activity and processivity but with reduced fidelity. In vivo, the pol1-L868M allele confers a mutator phenotype. This mutator phenotype is strongly increased upon inactivation of the 3′ exonuclease of pol δ but not that of pol ɛ. Several nonexclusive explanations are considered, including the hypothesis that the 3′ exonuclease of pol δ proofreads errors generated by pol α during initiation of Okazaki fragments. Given that eukaryotes encode specialized, proofreading-deficient polymerases with even lower fidelity than pol α [5], such intermolecular proofreading could be relevant to several DNA transactions that control genome stability