Function of CikA in the cyanobacterial circadian system: the pseudo-receiver domain of CikA regulates the circadian input pathway

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Title: Function of CikA in the cyanobacterial circadian system: the pseudo-receiver domain of CikA regulates the circadian input pathway
Author: Zhang, Xiaofan
Abstract: The circadian input kinase gene (cikA ) was first identified from a Tn5 mutant of Synechococcus elongatus PCC 7942 . A cikA null strain shows a striking phenotype related to circadian gene regulation : all sampled loci show a shortened circadian period and reduced amplitude of oscillation and a failure to exhibit a wild -type resetting of the phase of the rhythm after an environmental signal . This global defect in response to the environment suggests a key role for CikA in the circadian input pathways . Bioinformatics results classify CikA as a divergent member of the bacteriophytochrome family , suggesting a role in light signal transduction . In vitro analysis previously showed that CikA is a bona fide histidine protein kinase (HPK ) , and its kinase activity is regulated by the presence of other domains . Its own pseudo -receiver (PsR ) domain is not the cognate receiver domain of its kinase HPK domain , and its GAF domain does not likely bind a bilin chromophore as do photoreceptive phytochromes . Recent results suggested that CikA may function as a redox -sensor . In this study , we examined the function of each domain of CikA using different mutant cikA alleles , and determined their phenotypes with respect to complementation of a null mutant and overexpression in both wild type and cikA null strains . All domains except the featureless N -terminus were required for CikA function . Overexpression of all mutant alleles that encoded the PsR domain , whether or not the HPK was functional , caused a dominant arrhythmia phenotype . In the absence of PsR , overexpressed variants did not cause arrhythmia , but affected the amplitude and period of oscillation . The results suggest a model in which the PsR domain regulates kinase activity and mediates interaction with other input pathway components to allow CikA to reach the correct cellular position to fulfill its function . Cellular localization assays showed CikA can interact with a complex and showed a polar localization pattern , whereas its variant without PsR showed uniform distribution in the cell . In summary , CikA is an autoregulated kinase in which the PsR domain regulates activity of the HPK domain and also serves as an interaction module to lead the CikA to a specific cellular position .
URI: http : / /hdl .handle .net /1969 .1 /4261
Date: 2006-10-30

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Function of CikA in the cyanobacterial circadian system: the pseudo-receiver domain of CikA regulates the circadian input pathway. Available electronically from http : / /hdl .handle .net /1969 .1 /4261 .

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