Structural coupling of the inhibitory regions flanking the ETS domain of murine Ets-1

Several members of the ets gene family of transcription factors show negative regulation of DNA binding by intramolecular interactions. A structural mechanism for this auto-inhibition is investigated using a 161-residue N-terminal deletion mutant of murine Ets-1, Ets-1 Delta N280. This protein shows a similar reduced affinity for DNA as native Ets-1 because it contains the ETS domain in context of the flanking amino- and carboxy-terminal regions that together mediate repression of DNA binding. The secondary structure of Ets-1 Delta N280 was determined using NMR chemical shift, NOE, J coupling, and amide hydrogen exchange information. In addition to the winged helix-turn-helix ETS domain, Ets-1 Delta N280 contains two alpha-helices in the amino-terminal inhibitory region and one alpha-helix in the carboxy-terminal inhibitory region. Chemical shift comparisons were made between this protein and an activated form of Ets-1 lacking the amino-terminal inhibitory region. The spectral differences demonstrate that the amino- and carboxy-terminal inhibitory sequences are structurally coupled to one another, thus explaining the observation that both regions are required for the repression of DNA binding. Furthermore, these data show that the inhibitory sequences also interact directly with the first helix of the intervening ETS domain, thereby providing a pathway for the repression of DNA binding. These results lead to a model of an inhibitory module in Ets-1 composed of both the amino- and carboxy-terminal regions interfaced with the ETS domain. This establishes the structural framework for understanding the intramolecular inhibition of Ets-1 DNA binding.