A novel family of calmodulin-binding transcription activators in multicellular organisms.
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 (K(d) = 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.
Bouché
Nicolas
N
School of Biology, University of Leeds, Leeds LS2 9JT, United Kingdom.
Scharlat
Ariel
A
Snedden
Wayne
W
Bouchez
David
D
Fromm
Hillel
H
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis; D017173:Caenorhabditis elegans; D002147:Calmodulin / Q000737:chemistry* / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002846:Chromatography, Affinity; D003001:Cloning, Molecular; D017124:Conserved Sequence; D004247:DNA / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D019992:Databases as Topic; D004305:Dose-Response Relationship, Drug; D004330:Drosophila; D015723:Gene Library; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D007313:Insecta; D007700:Kinetics; D008957:Models, Genetic; D008969:Molecular Sequence Data; D005810:Multigene Family; D010455:Peptides / Q000737:chemistry; D010802:Phylogeny; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D020798:Two-Hybrid System Techniques; D001616:beta-Galactosidase / Q000378:metabolism
D002147:Calmodulin; D018076:DNA, Complementary; D010455:Peptides; D004247:DNA; D005982:Glutathione Transferase; D001616:beta-Galactosidase