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.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/4261 |
| Date | 30 October 2006 |
| Creators | Zhang, Xiaofan |
| Contributors | Golden, Susan S. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 991195 bytes, electronic, application/pdf, born digital |
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