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Palaeoanthropology: Did our ancestors
MIKE DAINTON Nature 410, 324 - 325 (2001)
Article Abstract: All African apes walk on their knuckles. There is no evidence for this behaviour in the earliest hominids, however, which conflicts with molecular DNA evidence suggesting that chimpanzees are more closely related to humans than to gorillas. On the basis of a multivariate analysis of four traits of the proximal wrist joint, Richmond and Strait claim that African apes and early hominids do share a common knuckle-walking ancestor. I propose that these traits are not uniquely associated with knuckle-walking and question the basis of their conclusion. It is still possible that no human ancestor knuckle-walked and that this behaviour evolved independently in different species.
Guard cell abscisic acid signalling
and engineering drought hardiness in plants
JULIAN I. SCHROEDER, JUNE M. KWAK & GETHYN J. ALLEN Nature 410, 327 - 330 (2001)
Article Abstract: Guard cells are located in the epidermis of plant leaves, and in pairs surround stomatal pores. These control both the influx of CO2 as a raw material for photosynthesis and water loss from plants through transpiration to the atmosphere. Guard cells have become a highly developed system for dissecting early signal transduction mechanisms in plants. In response to drought, plants synthesize the hormone abscisic acid, which triggers closing of stomata, thus reducing water loss. Recently, central regulators of guard cell abscisic acid signalling have been discovered. The molecular understanding of the guard cell signal transduction network opens possibilities for engineering stomatal responses to control CO2 intake and plant water loss.
Structure of the bacterial flagellar
protofilament and implications for a switch for supercoiling
FADEL A. SAMATEY, KATSUMI IMADA, SHIGEHIRO NAGASHIMA, FERENC VONDERVISZT, TAKASHI KUMASAKA, MASAKI YAMAMOTO & KEIICHI NAMBA Nature 410, 331 - 337 (2001)
Article Abstract: The bacterial flagellar filament is a helical propeller constructed from 11 protofilaments of a single protein, flagellin. The filament switches between left- and right-handed supercoiled forms when bacteria switch their swimming mode between running and tumbling. Supercoiling is produced by two different packing interactions of flagellin called L and R. In switching from L to R, the intersubunit distance (~52 Å) along the protofilament decreases by 0.8 Å. Changes in the number of L and R protofilaments govern supercoiling of the filament. Here we report the 2.0 Å resolution crystal structure of a Salmonella flagellin fragment of relative molecular mass 41,300. The crystal contains pairs of antiparallel straight protofilaments with the R-type repeat. By simulated extension of the protofilament model, we have identified possible switch regions responsible for the bi-stable mechanical switch that generates the 0.8 Å difference in repeat distance.
Copyright 2001 Macmillan Publishers Ltd. All rights reserved.
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