CALMODULIN ISOFORMS DIFFERENTIALLY ENHANCE THE BINDING OF CAULIFLOWERNUCLEAR PROTEINS AND RECOMBINANT TGA3 TO A REGION DERIVED FROM THE ARABIDOPSIS CAM-3 PROMOTER

Many stimuli increase cytoplasmic Ca2+ concentrations as an early sign al transduction event and alter the patterns of nuclear gene transcrip tion, but the mechanisms by which Ca2+ signals are transduced to the n ucleus are not known. This article shows that at least four DNA bindin g proteins from cauliflower nuclear extracts are also calmodulin (CaM) binding proteins. CaM enhances the binding of these proteins to a C/G -box sequence element in the Arabidopsis Cam-3 promoter. Binding to th e C/G-box is enhanced preferentially by the CaM isoform encoded by Cam -3. However, it is not clear whether the effect is mediated directly b y CaM or indirectly through the activity of a CaM-regulated protein ph osphatase. CaM also binds recombinant TGA3 and enhances its binding to the same Cam-3 promoter element. These results are consistent with th e idea that a Ca2+-mediated signaling pathway eliciting some changes i n gene expression may consist of CaM, or a structurally related Ca2+ b inding protein, and transcription factors.