DNA-BINDING PROPERTIES OF 2 ARABIDOPSIS MADS DOMAIN PROTEINS - BINDING CONSENSUS AND DIMER FORMATION

MADS domain proteins are members of a highly conserved family found in all eukaryotes. Genetic studies clearly indicate that many plant MADS domain proteins have different regulatory functions in flower develop ment, yet they share a highly conserved DNA binding domain and can bin d to very similar sequences. How, then, can these MADS box genes confe r their specific functions? Here, we describe results from DNA binding studies of AGL1 and AGL2 (for AGAMOUS-like), two Arabidopsis MADS dom ain proteins that are preferentially expressed in flowers, We demonstr ate that both proteins are sequence-specific DNA binding proteins and show that each binding consensus has distinct features, suggesting a m echanism for specificity. In addition, we show that the proteins with more similar amino acid sequences have more similar binding sequences. We also found that AGL2 binds to DNA in vitro as a dimer and determin ed the region of AGL2 that is sufficient for DNA binding and dimerizat ion. Finally, we show that several plant MADS domain proteins can bind to DNA either as homodimers or as heterodimers, suggesting that the n umber of different regulators could be much greater than the number of MADS box genes.