ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1988.tb00016.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractAfter describing briefly the work of Engelmann and Pfeffer about 100 years ago, the author presents the early history of bacterial chemotaxis in his laboratory since 1960. Then the report is brought up to the present by review of research in many laboratories including the author's.

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1988.tb00017.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractThe sensory transduction pathways between the transducing proteins and the switch on the flagellar motors have been investigated inEscherichia coliandSalmonella typhimurium. ATP, not GTP, is required for normal chemotaxis. A site of ATP action appears to be the conversion of an inactive form of the CheY protein to an active form, designated CheY*, that binds to the motor switch and initiates clockwise rotation. The methylation‐dependent and methylation‐independent pathways for chemotaxis have a common requirement for the CheA, CheW, and CheY proteins in addition to the switch and flagellar motor. It is concluded that the receptor/transducing proteins and the adaptation mechanism differ in the two types of pathway, but that other components of the transduction pathway are common to the methylation‐dependent and methylation‐independent p

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1988.tb00018.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractAnin vitroapproach to study bacterial motility and chemotaxis is described. The approach is based on a preparation of flagellated cell envelopes. The envelopes are prepared from bacteria by a penicillin treatment and subsequent osmotic lysis. When the envelopes are energized, their flagella rotate. The direction of rotation in wild type envelopes is counterclockwise. Inclusion of the CheY protein within the envelopes may restore clockwise rotation. The advantages and disadvantages of this approach are pointed out.

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1988.tb00019.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractHalobacteria detect changes in light intensity by retinal proteins, the number and identity of which are not yet unequivocally established. The sensory receptors are different from those for light energy conversion. The cells having no preferred swimming direction spontaneously reverse about every 10 s. An oscillator model has been proposed to explain this periodicity. Depending on wavelength and sign, a stimulus leads either to one prolonged interval between two reversals, the attractant response, or to a shortened interval, the repellent response. Sensory signals generated by stimulation of P‐565 and of P‐370 are integrated at a common link. Signals from other receptors may be processed by separate links. The nature of the sensory signals is not known, but the membrane potential can be excluded as a candidate. On the basis of the oscillator hypothesis the output signals of the integration links act on the oscillator and thus shift the time at which it triggers a reversal of the flagellar motor. Experiments indicate that cGMP and calcium play antagonistic roles in the oscillatory activity. Reversible methylation of specific membrane proteins influences the time during which successive signals are integrated. This reaction is assumed to terminate the lifetime of the excitatory signals and thus to allow the system to ad

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1988.tb00020.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractCyclic AMP (cAMP) has been shown to be a primary signal of the agglutination‐induced mating events of flagellar tip activation, cell wall loss, and mating structure activation in the unicellular algaChlamydomonas reinhardtii(Pasquale and Goodenough, Cell Biol. 105 (1987), 2279–2293). The flagellar membrane adenylate cyclase ofChlamydomonasis here shown to be inhibitedin vitroby EGTA, La3+, and trifluoperazine, and to be stimulated in the presence of calcium by incubation with exogenous calmodulin. Also, the motility of detergent‐extracted models ofChlamydomonasis shown to be enhanced by cAMP. These observations suggest the hypothesis that the twitching motility characteristic of agglutinatingChlamydomonasgametes may be signaled by cAMP produced locally within the flagella by a calmodulin‐sensitive adenylate

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1988.tb00021.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractDevelopment inDictyosteliumresults in the production of a multicellular aggregate. Aggregation depends on chemotaxis to cAMP and cell‐to‐cell relay of cAMP signalling. The cAMP signalling response involves surface receptor‐mediated GTP‐dependent activation of adenylate cyclase. Studies of the mutantsynag 7indicate that a soluble protein may be involved in this activation. Wild‐type supernatants are required to restore GTP‐dependent adenylate cyclase activity to mutant lysates.The surface cAMP receptor which initiates this response and is implicated in chemotaxis has been purified and an antiserum raised. The receptor undergoes a ligand‐induced mobility change, probably due to serine phosphorylation, when analyzed by SDS‐PAGE. Modulation of this transition is correlated with adaptation of the cells. Analysis of cells at various stages of development indicate that the receptor is most rapidly synthesized in the preaggregation stage. The antiserum was used to clone the cDNA for the receptor. Clones that have been sequenced account for about 33 000 D of the 37 000 D receptor. Hydropathy plots reveal 3 (or 4) potential membrane spanning domains; unsequenced regions are large enough to encode an additional 4 membrane spanning regions. Comparison to bovine rhodopsin reveals homology in those regions elucidated so far. Thirteen potential phosphorylation sites are present in the cytoplasmic domain and may be involved in ligand‐induce

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1988.tb00022.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractThe isolation of circadian clock mutants inNeurospora crassaandDrosophila melanogasterhave identified numerous genes whose function is necessary for the normal operation of the circadian clock. InNeurosporamany of these mutants map to a single locus calledfrq, whose properties suggest that its gene product is intimately involved in clock function. InDrosophilamutations at theperlocus also suggest a significant role for the product of this gene in the insect clock mechanism. Thepergene has been cloned and its gene product identified as a proteoglycan, most likely a membrane protein involved in affecting the ionic or electrical properties of cells in which it is located. Future progress in elucidating the mechanisms of circadian clocks are likely to come from continued analysis of clock mutants, both at the genetic and molecular levels.

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1988.tb00023.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractRecent literature on light‐induced changes in the distribution of growth and of endogenous growth regulators in the development of phototropic curvature is reviewed. It is concluded that in a great many cases the Cholodny‐Went hypothesis is sufficient to account for the growth changes bringing about curvature, though in certain dicotyledonous seedlings differential effects of light on the synthesis of growth inhibitors across the tissue from the lighted to the shaded side are implicated. The problems in the interpretation of results from experiments in which more than one photoresponse may be simultaneously induced are discussed and methods of circumventing them considered. Action spectroscopy suggests that dicotyledonous seedlings may have the same phototropic photoreceptor as monocotyledonous seedli

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1988.tb00024.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractOpening and closing of the stomatal pore is associated with very large changes in K‐salt accumulation in stomatal guard cells. This review discusses the ionic relations of guard cells in relation to the general pattern of transport processes in plant cells, in plasmalemma and tonoplast, involving primary active transport of protons, proton‐linked secondary active transport, and a number of gated ion channels. The evidence available suggests that the initiation of stomatal opening is regulated through the uptake mechanisms, whereas initiation of stomatal closing is regulated by control of ion efflux at the plasmalemma, and of fluxes to and from the vacuole. In response to a closing signal there are large transient increases in efflux of both Cl−(or Br−) and Rb+(K+) at the plasmalemma, with also a probable increase in anion flux from vacuole to cytoplasm and decrease in anion flux from cytoplasm to vacuole. A speculative hypothetical sequence of events is discussed, by which the primary response to a closing signal is an increase in Ca2+influx at the plasmalemma, producing depolarisation and increase in cytoplasmic Ca2+. The consequent opening of Ca2+‐sensitive Cl−channels, and voltage‐sensitive K+channels (also Ca2+‐sensitive?) in the plasmalemma, and of a Ca2+‐sensitive nonspecific channel in the tonoplast, could produce the flux effects identified by the tracer work; this speculation is also consistent with the Ca2+‐sensitivity of the response to closing signals and with evidence from patch clamping that such channels exist in at least some plant cells, though not yet all s

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1988.tb00025.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY