Extensive gene traffic on the mammalian X chromosome

Mammalian sex chromosomes have undergone profound changes since evolving from ancestral autosomes. By examining retroposed genes in the human and mouse genomes, we demonstrate that, during evolution, the mammalian X chromosome has generated and recruited a disproportionately high number of functional retroposed genes, whereas the autosomes experienced lower gene turnover. Most autosomal copies originating from X-linked genes exhibited testis-biased expression. Such export is incompatible with mutational bias and is likely driven by natural selection to attain male germline function. However, the excess recruitment is consistent with a combination of both natural selection and mutational bias.     

New early Jurassic tetrapod assemblages constrain Triassic-Jurassic tetrapod extinction event

The discovery of the first definitively correlated earliest Jurassic (200 million years before present) tetrapod assemblage (Fundy basin, Newark Supergroup, Nova Scotia) allows reevaluation of the duration of the Triassic-Jurassic tetrapod extinction event. Present are tritheledont and mammal-like reptiles, prosauropod, theropod, and ornithischian dinosaurs, protosuchian and sphenosuchian crocodylomorphs, sphenodontids, and hybodont, semionotid, and palaeonisciform fishes. All of the families are known from Late Triassic and Jurassic strata from elsewhere; however, pollen and spore, radiometric, and geochemical correlation indicate an early Hettangian age for these assemblages. Because all "typical Triassic" forms are absent from these assemblages, most Triassic-Jurassic tetrapod extinctions occurred before this time and without the introduction of new families. As was previously suggested by studies of marine invertebrates, this pattern is consistent with a global extinction event at the Triassic-Jurassic boundary. The Manicouagan impact structure of Quebec provides dates broadly compatible with the Triassic-Jurassic boundary and, following the impact theory of mass extinctions, may be implicated in the cause.     

Conversion of mesophilic to psychrophilic bacteria

The minimum temperature of growth of the mesophilic bacterium Pseudomonas aeruginosa has been significantly lowered from approximately 11 degrees to 0 degrees C. This shift in the minimum temperature of growth was accompanied by a corresponding decrease in the maximum temperature of growth. Transfer of this genetic characteristic by a transducing phage grown on a psychrophile or by ultraviolet mutagenesis was used to accomplish these shifts in range of growth temperature.     

Collagen synthesis: localization of prolyl hydroxylase in tendon cells detected with ferritin-labeled antibodies

An improved procedure was employed for linking ferritin to antibodies against prolyl hydroxylase, the enzyme that synthesizes the hydroxyproline in collagen. By electron microscopy, the enzyme was then found to be localized in cisternae of the rough endoplasmic reticulum of embryonic tendon cells; this indicates that hydroxylation of proline occurs while newly synthesized polypeptides are fed into the cisternae.     

Krinovite, NaMg2CrSi3O10: A New Meteorite Mineral

An unusual new silicate, krinovite, has been discovered within graphite nodules in three iron meteorites. Its ratio of silicon to oxygen of 3 : 10 suggests a rare kind of silicate polymerization. The meteorite nodules in which it occurs exhibit a chemical fractionation that differs from that of both stone meteorites and terrestrial basalt.