Howard C. Berg

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Statistical fluctuations limit the precision with which a microorganism can, in a given time T, determine the concentration of a chemoattractant in the surrounding medium. The best a cell can do is to monitor continually the state of occupation of receptors distributed over its surface. For nearly optimum performance only a small fraction of the surface(More)
Flagellated bacteria, such as Escherichia coli, swim by rotating thin helical filaments, each driven at its base by a reversible rotary motor, powered by an ion flux. A motor is about 45 nm in diameter and is assembled from about 20 different kinds of parts. It develops maximum torque at stall but can spin several hundred Hz. Its direction of rotation is(More)
Chemoreceptors in Escherichia coli are coupled to the flagella by a labile phosphorylated intermediate, CheY approximately P. Its activity can be inferred from the rotational bias of flagellar motors, but motor response is stochastic and limited to a narrow physiological range. Here we use fluorescence resonance energy transfer to monitor interactions of(More)
Bacteria swim by rotating flagellar filaments that are several micrometers long, but only about 20 nm in diameter. The filaments can exist in different polymorphic forms, having distinct values of curvature and twist. Rotation rates are on the order of 100 Hz. In the past, the motion of individual filaments has been visualized by dark-field or(More)
Responses of tethered cells of Escherichia coli to impulse, step, exponential-ramp or exponentiated sine-wave stimuli are internally consistent, provided that allowance is made for the nonlinear effect of thresholds. This result confirms that wild-type cells exposed to stimuli in the physiological range make short-term temporal comparisons extending 4 sec(More)
We prepared fusions of yellow fluorescent protein [the YFP variant of green fluorescent protein (GFP)] with the cytoplasmic chemotaxis proteins CheY, CheZ and CheA and the flagellar motor protein FliM, and studied their localization in wild-type and mutant cells of Escherichia coli. All but the CheA fusions were functional. The cytoplasmic proteins CheY,(More)
Bacterial chemotaxis is a model system for signal transduction, noted for its relative simplicity, high sensitivity, wide dynamic range and robustness. Changes in ligand concentrations are sensed by a protein assembly consisting of transmembrane receptors, a coupling protein (CheW) and a histidine kinase (CheA). In Escherichia coli, these components are(More)
In Escherichia coli chemotaxis, signaling depends on modulation of the level of phosphorylation of CheY, a small protein that couples receptors and flagellar motors. Working in vivo, we used fluorescence resonance energy transfer (FRET) to measure the interaction of CheY approximately P with its target, FliM. Binding of CheY approximately P to FliM was(More)
The Escherichia coli chemotaxis-signaling pathway computes time derivatives of chemoeffector concentrations. This network features modules for signal reception/amplification and robust adaptation, with sensing of chemoeffector gradients determined by the way in which these modules are coupled in vivo. We characterized these modules and their coupling by(More)