Nucleic Acids Research Advance Access originally published online on March 10, 2009
Nucleic Acids Research 2009 37(8):2723-2736; doi:10.1093/nar/gkp129
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Nucleic Acids Research, 2009, Vol. 37, No. 8 2723-2736
© 2009 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 |
Reconstitution of ‘floral quartets’ in vitro involving class B and class E floral homeotic proteins
Friedrich Schiller University Jena, Department of Genetics, Philosophenweg 12, D-07743 Jena, Germany
*To whom correspondence should be addressed. Tel: +49 3641 949 550; Fax: +49 3641 949 552; Email: guenter.theissen{at}uni-jena.de
Received October 31, 2008. Revised February 13, 2009. Accepted February 16, 2009.
Homeotic MADS box genes encoding transcription factors specify the identity of floral organs by interacting in a combinatorial way. The ‘floral quartet model’, published several years ago, pulled together several lines of evidence suggesting that floral homeotic proteins bind as tetramers to two separated DNA sequence elements termed ‘CArG boxes’ by looping the intervening DNA. However, experimental support for ‘floral quartet’ formation remains scarce. Recently, we have shown that the class E floral homeotic protein SEPALLATA3 (SEP3) is sufficient to loop DNA in floral-quartet-like complexes in vitro. Here, we demonstrate that the class B floral homeotic proteins APETALA3 (AP3) and PISTILLATA (PI) do only weakly, at best, form floral-quartet-like structures on their own. However, they can be incorporated into such complexes together with SEP3. The subdomain K3 of SEP3 is of critical importance for the DNA-bound heterotetramers to be formed and is capable to mediate floral quartet formation even in the sequence context of AP3 and PI. Evidence is presented suggesting that complexes composed of SEP3, AP3 and PI form preferentially over other possible complexes. Based on these findings we propose a mechanism of how target gene specificity might be achieved at the level of floral quartet stability.