Nucleic Acids Research Advance Access originally published online on November 25, 2008
Nucleic Acids Research 2009 37(1):144-157; doi:10.1093/nar/gkn900
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Nucleic Acids Research, 2009, Vol. 37, No. 1 144-157
© 2008 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Gene regulation, Chromatin and Epigenetics |
The class E floral homeotic protein SEPALLATA3 is sufficient to loop DNA in ‘floral quartet’-like complexes in vitro
1Department of Genetics, Friedrich Schiller University Jena, Philosophenweg 12, D-07743 Jena and 2Department of Molecular Plant Genetics, Max Planck Institute for Plant Breeding Research, Carl von Linné Weg 10, D-50829 Köln, Germany
*To whom correspondence should be addressed. Tel: +49 3641 949550; Fax: +49 3641 949 552; Email: guenter.theissen{at}uni-jena.de
Received October 1, 2008. Revised October 23, 2008. Accepted October 24, 2008.
The organs of a eudicot flower are specified by four functional classes, termed class A, B, C and E, of MADS domain transcription factors. The combinatorial formation of tetrameric complexes, so called ‘floral quartets’, between these classes is widely believed to represent the molecular basis of floral organ identity specification. As constituents of all complexes, the class E floral homeotic proteins are thought to be of critical relevance for the formation of floral quartets. However, experimental support for tetrameric complex formation remains scarce. Here we provide physico-chemical evidence that in vitro homotetramers of the class E floral homeotic protein SEPALLATA3 from Arabidopsis thaliana bind cooperatively to two sequence elements termed ‘CArG boxes’ in a phase-dependent manner involving DNA looping. We further show that the N-terminal part of SEPALLATA3 lacking K3, a subdomain of the protein–protein interactions mediating K domain, and the C-terminal domain, is sufficient for protein dimerization, but not for tetramer formation and cooperative DNA binding. We hypothesize that the capacity of class E MADS domain proteins to form tetrameric complexes contributes significantly to the formation of floral quartets. Our findings further suggest that the spacing and phasing of CArG boxes are important parameters in the molecular mechanism by which floral homeotic proteins achieve target gene specificity.
Present address: Wim Verelst, VIB Department of Plant Systems Biology, Ghent University, Technologiepark 927, B-9052 Ghent, Belgium
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