The gaseous phytohormone ethylene regulates various processes related to growth, development, and stress response of higher plants. A largely linear pathway of ethylene signaling was revealed by a number of molecular genetic studies. In the pathway, Ethylene-insensitive3 (EIN3) and EIN3-like (EIL) proteins are the key transcription factors. The EIN3/EIL proteins were shown to regulate expression of the GCC-box-binding transcription factors, ethylene-response factors. It is known that the phenotype of the Arabidopsis thaliana EIN3 (AtEIN3)-deficient mutants, e.g. long seedlings in the presence of ethylene or its precursor, is suppressed by overexpression of Arabidopsis EIL1 (AtEIL1) or EIL2 (AtEIL2), indicating the functional equivalence of these proteins.
In the present study, a region corresponding to the major DBD of the EIN3/EIL transcription factor family, which is the key factor in the ethylene signaling, was identified. The isolated domain exists in a monomeric form and retained the sequence specificity for the DNA binding. The structure determined by NMR spectroscopy consists of five alpha-helices, packing into a novel fold dissimilar to known DBDs. An NMR titration analysis suggested that a region including the key mutation site, ein3-3 site, was shown to be involved in DNA binding.
