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- Hit 252
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Novel Calmodulin-binding Proteins Involved in Multi-signal Transduction Pathways in Plants
- Date/Time : Mon., 15 July 2002
- Speaker : Dr. B.W. Poovaiah
- Washington State University
- Place : Life Science Bldg. #104
- For inquires : Professor Gynheung An Dept. of Life Science
생명과학과 안진흥 교수 (☎279-2176)
It is well established that calcium acts as an intracellular messenger in eukaryotes. Calmodulin (CaM), a ubiquitous and multifunctional Ca2+-binding protein, is a primary intracellular Ca2+ receptor, which transduces the second messenger Ca2+ signal by binding to and altering the activity of CaM-binding proteins. This laboratory has cloned and characterized several genes that encode for CaM-binding proteins. Among these genes is a chimeric Ca2+/CaM-dependent protein kinase (CCaMK) which is characterized by the presence of a kinase domain, an autoinhibitory domain, a CaM-binding domain and a neural visinin-like Ca2+-binding domain in a single polypeptide. One of the unique features of CCaMK is the presence of a visinin-like Ca2+-binding domain, an additional Ca2+ sensing mechanism not previously known to exist in kinases. Recently, we have characterized a novel Ca2+/CaM-regulated CGCG box DNA-binding protein family involved in multi-signal transduction pathways in plants. These genes (AtSR1-6) possess unique structural features that include: a CaM-binding domain, a DNA-binding domain and ankyrin repeats. These six genes are rapidly and differentially induced by environmental signals such as heat shock, cold, UVB, gravity, salt and wounding; hormones such as ethylene and abscisic acid; and signal molecules such as methyl jasmonate, hydrogen peroxide and salicylic acid. Hence they are called Arabidopsis thaliana signal-responsive genes. Ca2+/CaM binds to all AtSRs, and their CaM-binding regions are located on a conserved basic amphiphilic a-helical motif in the C-terminus. AtSR1 targets the nucleus, and specifically recognizes a novel 6-bp CGCG box, (A/C/G)CGCG(G/T/C). The multiple CGCG cis-elements are found in promoters of genes such as those involved in ethylene signaling, ABA signaling and light signal perception. The DNA-binding domain in AtSR1 is located on N-terminal 146 bp where all AtSR1 related proteins share high homology, but exhibit no homology to other known DNA-binding proteins. The CaM-binding nuclear proteins isolated from the wounded leaves exhibit high and specific CGCG box DNA-binding activities. The T-DNA insertion knockout mutants show altered growth patterns. These results suggest that the AtSR gene family encodes a novel type of Ca2+/CaM-regulated DNA-binding proteins involved in multiple signal transduction pathways in plants.