SummaryVibrio cholerae has three sets of chemotaxis-related signaling proteins, of which only System II has been shown to be involved in chemotaxis. Here, we examined localization of green fluorescent protein (GFP)-fused components of System I. The histidine kinase (CheA1) and the adaptor (CheW0) of System I localized to polar and lateral membrane regions with standing incubation (microaerobic conditions), but their localization was lost after shaking (aerobic conditions). A transmembrane receptor of System I also showed polar and lateral localization with standing incubation. By contrast, GFP-fused components of System II localized constitutively to the flagellated pole. Nitrogen gas, sodium azide or carbonylcyanide m-chlorophenylhydrazone induced localization of CheA1-GFP even with shaking incubation, suggesting that the localization is controlled in response to changes in energy metabolism. Fluorescently labeled tetracysteine-tagged CheA1 also showed azideinduced localization, arguing against artifactual effects of GFP fusions. These results suggest that System I components are assembled into the supramolecular signaling complex in response to reduced cellular energy states, raising the possibility that the System I complex plays a role in sensing and signaling under microaerobic environments, such as in the host intestine.

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Abstract-The complete genome sequence of V. cholerae has revealed the presence of four CheV's, namely putative CheV, CheV1, CheV2 and CheV3, along with the three chemotaxis-related signaling systems designated as System I, II and III. To determine the roles of the CheV proteins, whose genes are located outside of the che gene clusters, we examined their cellular localization and then their roles in chemotaxis. Among the four CheV's, CheV1 plays a major role in chemotaxis as observed with swarm assay and fluorescence microscopy, suggesting its involvement in System II.

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Liye-cell imaging and analysis of cAMP-induced cAMP response ;n Dictyostetium using microfluidics chambers Fumihito Fukujini, Keita Kaminoi, Satoshi Sawaii'2'] (iGnadttate Schooi of' Arts andScienees, Universitv. ofTbk}'e, !Reseat'ch Center.for thmplex S.vstems Biology, Uhiversit.v (ijr 7bkyo, ]PRESTO, Japan Science and 71ichnoiog}' Agency)Transient synthesis and secretion of cyclic AMP {cAMP) induced by extracellular cAMP mediates interce]]ular signa]ing during aggregation of Dictyosteiium. The response is characterized by a fast initia] peak that appears about 1inin after exposure to an increase in extraeellular cAMP fo11owed by dose-dependent attenuation to the pre-stimu]us level. There is a]so a fast oscillatory component of about