title: Identification of a calmodulin-binding NAC protein as a transcriptional repressor in Arabidopsis.
abstract: Calmodulin (CaM), a ubiquitous calcium-binding protein, regulates diverse cellular functions by modulating the activity of a variety of proteins. However, little is known about how CaM directly regulates transcription. Screening of an Arabidopsis cDNA expression library using horseradish peroxidase-conjugated calmodulin as a probe identified a calmodulin-binding NAC protein (CBNAC). Using gel overlay assays, a Ca2+-dependent CaM-binding domain was identified in the C terminus of this protein. Specific binding of CaM to CaM-binding domain was corroborated by site-directed mutagenesis and a split-ubiquitin assay. Using a PCR-mediated random binding site selection method, we identified a DNA-binding sequence (CBNACBS) for CBNAC, which consisted of a GCTT core sequence flanked on both sides by other frequently repeating sequences (TTGCTTANNNNNNAAG). CBNAC was able to bind to CBNACBS, which resulted in the repression of transcription in Arabidopsis protoplasts. Interestingly, the transcriptional repression mediated by CBNAC was enhanced by CaM. These results suggest that CBNAC may be a CaM-regulated transcriptional repressor in Arabidopsis.
authors.affiliation: Division of Applied Life Science (BK21 Program), Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju 660-701, Korea.
authors.forename: Ho Soo
authors.initials: HS
authors.lastname: Kim
authors.forename: Byung Ouk
authors.initials: BO
authors.lastname: Park
authors.forename: Jae Hyuk
authors.initials: JH
authors.lastname: Yoo
authors.forename: Mi Soon
authors.initials: MS
authors.lastname: Jung
authors.forename: Sang Min
authors.initials: SM
authors.lastname: Lee
authors.forename: Hay Ju
authors.initials: HJ
authors.lastname: Han
authors.forename: Kyung Eun
authors.initials: KE
authors.lastname: Kim
authors.forename: Sun Ho
authors.initials: SH
authors.lastname: Kim
authors.forename: Chae Oh
authors.initials: CO
authors.lastname: Lim
authors.forename: Dae-Jin
authors.initials: DJ
authors.lastname: Yun
authors.forename: Sang Yeol
authors.initials: SY
authors.lastname: Lee
authors.forename: Woo Sik
authors.initials: WS
authors.lastname: Chung
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D002147:Calmodulin / Q000235:genetics / Q000378:metabolism; D002148:Calmodulin-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D015723:Gene Library; D011485:Protein Binding / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000502:physiology; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D020218:Response Elements / Q000502:physiology; D014158:Transcription, Genetic / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; C577034:CBNAC protein, Arabidopsis; D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D004268:DNA-Binding Proteins; D012097:Repressor Proteins