Journal Article

A <i>Synechocystis</i> Homolog of SipA Protein, Ssl3451, Enhances the Activity of the Histidine Kinase Hik33

Tasuku Sakayori, Yoshihiro Shiraiwa and Iwane Suzuki

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 50, issue 8, pages 1439-1448
Published in print August 2009 | ISSN: 0032-0781
Published online June 2009 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcp089
A Synechocystis Homolog of SipA Protein, Ssl3451, Enhances the Activity of the Histidine Kinase Hik33

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  • Molecular and Cell Biology
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In the cyanobacterium Synechocystis sp. PCC 6803, the histidine kinase Hik33 regulates the expression of several stress-inducible genes. Recently, a yeast two-hybrid screen revealed a specific interaction between Hik33 and a small protein, Ssl3451. To investigate the function of Ssl3451, we developed an assay to monitor the autophosphorylation of Hik33 in vitro. Addition of Ssl3451 to the reaction mixture dramatically enhanced the autophosphorylation activity of Hik33. Pulse–chase experiments revealed that Ssl3451 stimulated the autophosphorylation of Hik33 but did not affect its dephosphorylation. These findings indicated that Ssl3451 might be an activator of Hik33. When the amount of Hik33 was kept constant and the amount of Ssl3451 was increased in the reaction mixture, the extent of autophosphorylation of Hik33 reached a plateau when equimolar concentrations were present, suggesting that Ssl3451 enhances the activity of Hik33 by associating with it with a 1 : 1 stoichiometry. Disruption of the gene for Ssl3451 resulted in increased expression of the hliB gene, which is induced by Hik33 under standard growth conditions, but it did not affect the levels of the hliB mRNA at low temperature. Together, these results suggest that Ssl3451 might enhance the activity of Hik33 both in vitro and in vivo.

Keywords: Autophosphorylation; Cyanobacterium; Gene expression; Response regulator; Signal transduction; Two-component system

Journal Article.  6022 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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