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J. Biol. Chem., Vol. 277, Issue 6, 4206-4214, February 8, 2002

This Article Full Text Full Text (PDF) All Versions of this Article: 277/6/4206    most recent M104595200v1 Submit a Letter to Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Reddy, A. S. N. Articles by Harnly, M. J. Search for Related Content PubMed PubMed Citation Articles by Reddy, A. S. N. Articles by Harnly, M. J. Social Bookmarking                      What's this?

Isolation and Characterization of a Novel Calmodulin-binding Protein from Potato^*

Anireddy S. N. Reddy, Irene S. Day, S. B. Narasimhulu, Farida Safadi, Vaka S. Reddy, Maxim Golovkin, and Melissa J. Harnly

From the Department of Biology and Program in Cell and Molecular Biology, Colorado State University, Fort Collins, Colorado 80523

Tuberization in potato is controlled by hormonal and environmental signals. Ca²⁺, an important intracellular messenger, and calmodulin (CaM), one of the primary Ca²⁺ sensors, have been implicated in controlling diverse cellular processes in plants including tuberization. The regulation of cellular processes by CaM involves its interaction with other proteins. To understand the role of Ca²⁺/CaM in tuberization, we have screened an expression library prepared from developing tubers with biotinylated CaM. This screening resulted in isolation of a cDNA encoding a novel CaM-binding protein (potato calmodulin-binding protein (PCBP)). Ca²⁺-dependent binding of the cDNA-encoded protein to CaM is confirmed by ³⁵S-labeled CaM. The full-length cDNA is 5 kb long and encodes a protein of 1309 amino acids. The deduced amino acid sequence showed significant similarity with a hypothetical protein from another plant, Arabidopsis. However, no homologs of PCBP are found in nonplant systems, suggesting that it is likely to be specific to plants. Using truncated versions of the protein and a synthetic peptide in CaM binding assays we mapped the CaM-binding region to a 20-amino acid stretch (residues 1216-1237). The bacterially expressed protein containing the CaM-binding domain interacted with three CaM isoforms (CaM2, CaM4, and CaM6). PCBP is encoded by a single gene and is expressed differentially in the tissues tested. The expression of CaM, PCBP, and another CaM-binding protein is similar in different tissues and organs. The predicted protein contained seven putative nuclear localization signals and several strong PEST motifs. Fusion of the N-terminal region of the protein containing six of the seven nuclear localization signals to the reporter gene -glucuronidase targeted the reporter gene to the nucleus, suggesting a nuclear role for PCBP.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank^TM/EBI Data Bank with accession number(s) AF378084.

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