A Novel Family of Calmodulin-binding Transcription
Activators in Multicellular Organisms*
Nicolas
Bouché
§,
Ariel
Scharlat¶,
Wayne
Snedden
,
David
Bouchez§, and
Hillel
Fromm**
From the School of Biology, University of Leeds,
Leeds LS2 9JT, United Kingdom, the
Department of Plant Sciences, Tel Aviv
University, Tel Aviv 69978, Israel, ¶ Weizmann Institute of
Science, Plant Science Department, Rehovot 76100, Israel,
Queen's University, Department of Biology, Kingston, Ontario
K7L 3N6, Canada, and § Institut National de la Recherche
Agronomique, Station de Génétique,
Versailles 78026, France
Screening of cDNA expression
libraries derived from plants exposed to stress, with
35S-labeled recombinant calmodulin as a probe,
revealed a new family of proteins containing a transcription activation
domain and two types of DNA-binding domains designated the CG-1 domain
and the transcription factor immunoglobulin domain, ankyrin repeats,
and a varying number of IQ calmodulin-binding motifs. Based on
domain organization and amino acid sequence comparisons, similar
proteins, with the same domain organization, were identified in the
genomes of other multicellular organisms including human,
Drosophila, and Caenorhabditis, whereas none
were found in the complete genomes of single cell eukaryotes and
prokaryotes. This family of proteins was designated calmodulin-binding
transcription activators (CAMTAs). Arabidopsis thaliana
contains six CAMTA genes (AtCAMTA1-AtCAMTA6). The
transcription activation domain of AtCAMTA1 was mapped by testing a
series of protein fusions with the DNA-binding domain of the bacterial
LexA transcription factor and two reporter genes fused to LexA
recognition sequences in yeast cells. Two human proteins designated
HsCAMTA1 and HsCAMTA2 were also shown to activate transcription in
yeast using the same reporter system. Subcellular fractionation of
Arabidopsis tissues revealed the presence of CAMTAs
predominantly in the nucleus. Calmodulin binding assays identified a
region of 25 amino acids capable of binding calmodulin with high
affinity (Kd = 1.2 nM) in the presence
of calcium. We suggest that CAMTAs comprise a conserved family of
transcription factors in a wide range of multicellular eukaryotes,
which possibly respond to calcium signaling by direct binding of calmodulin.
*
This work was supported in part by a grant from the
Biotechnology and Biological Sciences Research Council, UK (to H. F.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EBI Data Bank with accession number(s) AF491304.
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