A late Eemian aridity pulse in central Europe during the last glacial inception

Investigating the processes that led to the end of the last interglacial period is relevant for understanding how our ongoing interglacial will end, which has been a matter of much debate (see, for example, refs 1, 2). A recent ice core from Greenland demonstrates climate cooling from 122,000 years ago driven by orbitally controlled insolation, with glacial inception at 118,000 years ago. Here we present an annually resolved, layer-counted record of varve thickness, quartz grain size and pollen assemblages from a maar lake in the Eifel (Germany), which documents a late Eemian aridity pulse lasting 468 years with dust storms, aridity, bushfire and a decline of thermophilous trees at the time of glacial inception. We interpret the decrease in both precipitation and temperature as an indication of a close link of this extreme climate event to a sudden southward shift of the position of the North Atlantic drift, the ocean current that brings warm surface waters to the northern European region. The late Eemian aridity pulse occurred at a 65 degrees N July insolation of 416 W m(-2), close to today's value of 428 W m(-2) (ref. 9), and may therefore be relevant for the interpretation of present-day climate variability.     

Cloning of bovine GAP and its interaction with oncogenic ras p21

The plasma membrane-bound mammalian ras proteins of relative molecular mass 21,000 (ras p21) share biochemical and structural properties with other guanine nucleotide-binding regulatory proteins (G-proteins). Oncogenic ras p21 variants result from amino acid substitutions at specific positions that cause p21 to occur predominantly complexed to GTP in vivo. Recently, a GTPase activating protein (GAP) with cytosolic activity has been discovered that stimulates the GTPase activity of normal but not of oncogenic ras p21. GAP might be either a negative regulatory agent which acts further upstream in the regulatory pathway or the downstream target of ras p21. We have identified a protein from bovine brain with apparent relative molecular mass 125,000 that has GAP activity. Here, using pure GAP in a kinetic competition assay, we show that GAP interacts preferentially with the active GTP complexes of both normal and oncogenic Harvey (Ha) ras p21 compared with the inactive GDP complexes. We also report the cloning and sequencing of the complementary DNA for bovine GAP. Regions of GAP share amino acid similarity with the noncatalytic domain of adenylate cyclase from the yeast Saccharomyces cerevisiae and with regions conserved between phospholipase C-148, the crk oncogene product and the nonreceptor tyrosine kinases.