DNA-BINDING PROPERTIES OF ARABIDOPSIS MADS DOMAIN HOMEOTIC PROTEINS APETALA1, APETALA3, PISTILLATA AND AGAMOUS

The MADS domain proteins APETALA1 (AP1), APETALA3 (AP3), PISTILLATA (P I), and AGAMOUS (AG) specify the identity of Arabidopsis floral organs , AP1 and AG homocomplexes and AP3-PI heterocomplexes bind to CArG-box sequences, The DNA-binding properties of these complexes were investi gated. We find that AP1, AG and AP3-PI are all capable of recognizing the same DNA-binding sites, although with somewhat different affinitie s, In addition, the three complexes induce similar conformational chan ges on a CArG-box sequence. Phasing analysis reveals that the induced distortion is DNA bending, oriented toward the minor groove. The molec ular dissection of AP1, AP3, PI and AG indicates that the boundaries o f the dimerization domains of these proteins vary, The regions require d to form a DNA-binding complex include, in addition to the MADS box, the entire L region (which follows the MADS box) and the first putativ e amphipathic helix of the K box in the case of AP3-PI, while for AP1 and AG only a part of the L region is needed. The similarity of the DN A-binding properties of AP1, AP3-PI and AG is discussed with regard to the biological specificity that these proteins exhibit.