The APETALA2 domain is related to a novel type of DNA binding domain.

The recently cloned APE TALA2 (AP2) gene regulates meristem identity, floral organ specification, and seed coat development in Arabidopsis (Bowman et al., 1989, 1991; Kunst et al., 1989; lrish and Sussex, 1990; Jofuku et al., 1994). The deduced AP2 amino acid sequence is different from that of other floral regulatory proteins, most of which share the same type of DNA binding motif, the MADS domain (for review, see Davies and Schwarz-Sommer, 1994). Although AP2 does not have a MADS domain, it contains two copies of a nove1 motif, dubbed the AP2 domain, which is also found in other plant genes without known function (Jofuku et al., 1994). It has been suggested that a conserved core region of the AP2 domain forms an amphipathic helix that mediates protein-protein interactions. The additional presence of a putative nuclear localization signal and of an acidic and serine-rich region outside the AP2 domain have been taken as evidente for AP2 being a transcriptional regulator (Jofuku et al., 1994). Ohme-Takagi and Shinshi (1995) have now identified a small family of tobacco proteins that bind to the ethyleneresponsive elements of genes encoding pathogenesis-related proteins. The amino acid sequences of the ethylene-responsive element binding proteins (EREBPs) are rather divergent, except for an -60-amino acid long domain that is highlyconserved among all family members. This conserved domain is coincident with the DNA binding domain of EREBPs, as demonstrated by deletion analyses. Ohme-Takagi and Shinshi (1995) noted that the EREBP domain ís alsofound in a number of plant genes without known function. Sequence comparison shows that the EREBP DNA binding domain and theAP2 domain are closely related (Figure l), suggesting that the AP2 domain also binds DNA. In contrast to the four published EREBPs, AP2 would appear to contain two DNA binding domains. However, there are precedents for the presence of more than one DNA binding domain in a single pro-