David Lesser Mitchell

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The persistence of bacterial DNA over geological timespans remains a contentious issue. In direct contrast to in vitro based predictions, bacterial DNA and even culturable cells have been reported from various ancient specimens many million years (Ma) old [1–8]. As both ancient DNA studies and the revival of microorganisms are known to be susceptible to(More)
in characterizing ice crystal shape and particle size distribution in optically thin ice clouds. U pper-tropospheric ice clouds are important modulators of the Earth's climate, cover 20% of the globe at any given time (Liou 1986), and occur ~43% of the time in long-term satellite datasets (Wylie and Menzel 1999). Ice clouds, such as cirrus, tend to reflect(More)
Diagenesis was studied in DNA obtained from Siberian permafrost (permanently frozen soil) ranging from 10,000 to 400,000 years in age. Despite optimal preservation conditions, we found the sedimentary DNA to be severely modified by interstrand crosslinks; single- and double-stranded breaks; and freely exposed sugar, phosphate, and hydroxyl groups.(More)
1. An important target for conservation planning is the minimum amount of habitat needed in a landscape to ensure the persistence of a species. Appropriate targets can be determined by identifying thresholds in the amount of habitat, below which persistence, abundance or occupancy declines rapidly. Although some studies have identified habitat thresholds,(More)
Chromatin structure is known to be a barrier to DNA repair and a large number of studies have now identified various factors that modify histones and remodel nucleosomes to facilitate repair. In response to ultraviolet (UV) radiation several histones are acetylated and this enhances the repair of DNA photoproducts by the nucleotide excision repair (NER)(More)
Experimental animal models are extremely valuable for the study of human diseases, especially those with underlying genetic components. The exploitation of various animal models, from fruitflies to mice, has led to major advances in our understanding of the etiologies of many diseases, including cancer. Cutaneous malignant melanoma is a form of cancer for(More)
The ultraviolet radiation present in sunlight is immune suppressive. Recently we showed that solar-simulated ultraviolet radiation (ultraviolet A + B; 295-400 nm), applied after immunization, suppressed immunologic memory and the elicitation of delayed-type hypersensitivity to the common opportunistic pathogen, Candida albicans. Further, we found that(More)
We have surveyed the biologically harmful radiation penetrating the water column along a transect in the western Gulf of Mexico using dosimeters consisting of intact viruses or naked calf-thymus DNA (ctDNA). The indigenous marine bacteriophage PWH3a-P1, which lytically infects the heterotrophic bacterium Vibrio natriegens (strain PWH3a), displayed decay(More)
We report on the complex nature of the induced Martian magnetotail using simultaneous magnetic field and plasma measurements from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. Two case studies are analyzed from which we identify (1) repetitive loading and unloading of tail magnetic flux as the field magnitude changes dramatically,(More)
Like many structured RNAs, the Tetrahymena group I intron ribozyme folds through multiple pathways and intermediates. Under standard conditions in vitro, a small fraction reaches the native state (N) with kobs ≈ 0.6 min(-1), while the remainder forms a long-lived misfolded conformation (M) thought to differ in topology. These alternative outcomes reflect a(More)