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SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION

Calmodulin Interacts with and Regulates the RNA-Binding Activity of an Arabidopsis Polyadenylation Factor Subunit^1,[OA]

Department of Plant and Soil Sciences, University of Kentucky, Lexington, Kentucky 40546–0312 (K.J.D., J.Z., K.-Y.Y., D.L.F., A.G.H.); Department of Botany, Miami University, Oxford, Ohio 45056 (R.X., Q.Q.L.); and Department of Biological Sciences, University of Massachusetts, Lowell, Massachusetts 01845 (K.-Y.Y., D.L.F.)

The Arabidopsis (Arabidopsis thaliana) gene that encodes the probable ortholog of the 30-kD subunit of the mammalian cleavage and polyadenylation specificity factor (CPSF) is a complex one, encoding small (approximately 28 kD) and large (approximately 68 kD) polypeptides. The small polypeptide (AtCPSF30) corresponds to CPSF30 and is the focus of this study. Recombinant AtCPSF30 was purified from Escherichia coli and found to possess RNA-binding activity. Mutational analysis indicated that an evolutionarily conserved central core of AtCPSF30 is involved in RNA binding, but that RNA binding also requires a short sequence adjacent to the N terminus of the central core. AtCPSF30 was found to bind calmodulin, and calmodulin inhibited the RNA-binding activity of the protein in a calcium-dependent manner. Mutational analysis showed that a small part of the protein, again adjacent to the N terminus of the conserved core, is responsible for calmodulin binding; point mutations in this region abolished both binding to and inhibition of RNA binding by calmodulin. Interestingly, AtCPSF30 was capable of self-interactions. This property also mapped to the central conserved core of the protein. However, calmodulin had no discernible effect on the self-association. These results show that the central portion of AtCPSF30 is involved in a number of important functions, and they raise interesting possibilities for both the interplay between splicing and polyadenylation and the regulation of these processes by stimuli that act through calmodulin.

² These authors contributed equally to the paper.

³ Present address: Department of Surgery, University of Wisconsin-Madison, 600 Highland Ave., Madison, WI 53792.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Arthur G. Hunt (aghunt00{at}uky.edu).

^[OA] Open Access articles can be viewed online without a subscription.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.070672.

^* Corresponding author; e-mail aghunt00{at}uky.edu; fax 859–257–7125.

Received September 29, 2005; returned for revision December 20, 2005; accepted January 27, 2006.

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