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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Identification of Three Urease Accessory Proteins That Are Required for Urease Activation in Arabidopsis¹

Freie Universität Berlin, Institut für Biologie, Abteilung Biochemie der Pflanzen, 14195 Berlin, Germany (C.-P.W., T.R.); and GABI-Kat at Max-Planck-Institute for Plant Breeding Research, 50829 Cologne, Germany (M.G.R.)

Urease is a nickel-containing urea hydrolase involved in nitrogen recycling from ureide, purine, and arginine catabolism in plants. The process of urease activation by incorporation of nickel into the active site is a prime example of chaperone-mediated metal transfer to an enzyme. Four urease accessory proteins are required for activation in Klebsiella aerogenes. In plants urease accessory proteins have so far been only partially defined. Using reverse genetic tools we identified four genes that are necessary for urease activity in Arabidopsis (Arabidopsis thaliana; ecotypes Columbia and Nössen). Plants bearing T-DNA or Ds element insertions in either the structural gene for urease or in any of the three putative urease accessory genes AtureD, AtureF, and AtureG lacked the corresponding mRNAs and were defective in urease activity. In contrast to wild-type plants, the mutant lines were not able to support growth with urea as the sole nitrogen source. To investigate whether the identified accessory proteins would be sufficient to support eukaryotic urease activation, the corresponding cDNAs were introduced into urease-negative Escherichia coli. In these bacteria, urease activity was observed only when all three plant accessory genes were coexpressed together with the plant urease gene. Remarkably, plant urease activation occurred as well in cell-free E. coli extracts, but only in extracts from cells that had expressed all three accessory proteins. The future molecular dissection of the plant urease activation process may therefore be performed in vitro, providing a powerful tool to further our understanding of the biochemistry of chaperone-mediated metal transfer processes in plants.

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: Claus-Peter Witte (cpwitte{at}zedat.fu-berlin.de).

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.070292.

^* Corresponding author; e-mail cpwitte{at}zedat.fu-berlin.de; fax 49–30–83853372.

Received August 24, 2005; returned for revision September 15, 2005; accepted September 19, 2005.

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