The lumen of the endoplasmic reticulum contains a number of distinct molecular chaperones and folding factors, which modulate the folding and assembly of newly synthesized proteins and protein complexes. A subset of these luminal components are specific for glycoproteins, and, like calnexin and calreticulin, the thioldependent reductase ERp57 has been shown to interact specifically with soluble secretory proteins bearing Nlinked carbohydrate.Calnexin and calreticulin also interact with glycosylated integral membrane proteins, and in this study we have examined the interaction of ERp57 with these substrates. As with soluble proteins, the binding of ERp57 to an integral membrane protein is dependent upon the protein bearing an N-glycan that has undergone glucose trimming. Furthermore, ERp57 binds to newly synthesized glycoproteins in combination with either calnexin or calreticulin. We propose that ERp57 acts in concert with calnexin and calreticulin to modulate glycoprotein folding and enforce the glycoprotein specific quality control mechanism operating in the endoplasmic reticulum. The endoplasmic reticulum (ER)1 is a major site of protein synthesis, producing both secretory and integral membrane proteins. After insertion into, or translocation across, the membrane of the ER, newly synthesized proteins often require the assistance of folding enzymes and molecular chaperones to assist subsequent folding and oligomeric assembly (1, 2). Many chaperones specifically associate with newly synthesized proteins, apparently by recognizing specific features present in the incompletely folded or assembled polypeptide (3, 4).Calnexin, an integral membrane protein, and calreticulin, its luminal homologue, are two ER-resident molecular chaperones that have been shown to bind selectively and transiently to glycoproteins that carry asparagine-linked carbohydrate side chains (5-7). More precisely, calnexin and calreticulin interact specifically with the monoglucosylated form of the oligosaccharide (8 -10), leading to retention of the glycoprotein within the ER (11). The monoglucosylated glycans are generated by the action of glucosidases I and II, which rapidly remove two of the three glucoses from the mannose-rich oligosaccharide core (12). Slow removal of the final glucose by glucosidase II allows the release of the glycoprotein by calnexin and calreticulin. The re-addition of a single, terminal, glucose residue by UDP-glucose:glycoprotein glucosyltransferase (13, 14) occurs when a glycoprotein has not attained its correctly folded state, thus regenerating a monoglucosylated glycan. In this way a cycle of de-and reglucosylation acts to modulate the association of calnexin and calreticulin (8, 12), allowing the selective binding and retention of incompletely folded or assembled glycoproteins within the ER. Hence, calnexin, calreticulin, and UDP-glucose: glycoprotein glucosyltransferase are believed to constitute a "quality control" step for newly synthesized glycoproteins prior to their exit from the ER (11,12,15).We have rece...

Abstract:Stratigraphic and geomorphic evidence indicate floods that occur soon after forest fires have been intermittent but common events in many mountainous areas during the past several thousand years. The magnitude and recurrence of these post-fire flood events reflects the joint probability between the recurrence of fires and the recurrence of subsequent rainfall events of varying magnitude and intensity. Following the May 1996 Buffalo Creek, Colorado, forest fire, precipitation amounts and intensities that generated very little surface runoff outside of the burned area resulted in severe hillslope erosion, floods, and streambed sediment entrainment in the rugged, severely burned, 48 km 2 area. These floods added sediment to many existing alluvial fans, while simultaneously incising other fans and alluvial deposits. Incision of older fans revealed multiple sequences of fluvially transported sandy gravel that grade upward into charcoal-rich, loamy horizons. We interpret these sequences to represent periods of high sediment transport and aggradation during floods, followed by intervals of quiescence and relative stability in the watershed until a subsequent fire occurred.An alluvial sequence near the mouth of a tributary draining a 0Ð82 km 2 area indicated several previous post-fire flood cycles in the watershed. Dendrochronologic and radiocarbon ages of material in this deposit span approximately 2900 years, and define three aggradational periods. The three general aggradational periods are separated by intervals of approximately nine to ten centuries and reflect a 'millennium-scale' geomorphic response to a closely timed sequence of events: severe and intense, watershed-scale, stand-replacing fires and subsequent rainstorms and flooding. Millennium-scale aggradational units at the study site may have resulted from a scenario in which the initial runoff from the burned watershed transported and deposited large volumes of sediment on downstream alluvial surfaces and tributary fans. Subsequent storm runoff may have produced localized incision and channelization, preventing additional vertical aggradation on the sampled alluvial deposit for several centuries. Two of the millennium-scale aggradational periods at the study site consist of multiple gravel and loam sequences with similar radiocarbon ages. These closely dated sequences may reflect a 'multidecade-scale' geomorphic response to more frequent, but aerially limited and less severe fires, followed by rainstorms of relatively common recurrence. Published in

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Lava Falls Rapid is the most formidable reach of whitewater on the Colorado River in Grand Canyon and is one of the most famous rapids in the world. Once thought to be controlled o River floods (less than 3,540 m /s) removed most of the deposition at the mouth of Prospect Canyon within 3 years after debris flows in 1939, 1954, and 1955. Releases in 1965 from Glen Canyon Dam that were above powerplant capacity but less than 1,640 m3/s removed most of the debris fan

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