The proto-oncoprotein c-Ets1 is a well-known transcription factor that belongs to the Ets family and plays a role in haematopoietic differentiation, angiogenesis, and carcinogenesis. Ets family members share a unique DNA binding domain, the Ets domain, and are known to control DNA binding activity and transcriptional activation by autoinhibition. In c-Ets1 the DNA binding domain as well as N-terminal and C-terminal inhibitory domains are involved in autoinhibitory regulation. It has been proposed that intramolecular interactions are part of the autoinhibitory mechanism. We applied a GST pull-down assay as well as a two-hybrid system in yeast to show an interaction between the DNA binding domain of c-Ets1 and a domain N-terminal thereof. We have mapped the interaction sites within both of the c-Ets1 domains. Comparison of the analogous intramolecular interaction in c-Ets1 and in v-Ets revealed that the interaction we detected is stronger in v-Ets than in c-Ets1. In view of previous findings from DNA binding studies, and kinetic experiments as well as structural data, our results suggest a new model as to how intramolecular interactions might participate in the regulation of DNA binding. Binding of c-Ets1 to DNA temporarily changes the intramolecular pattern of interaction in c-Ets1, leading to an increase in affinity of c-Ets1 to DNA. In full-length c-Ets1 the intramolecular interactions re-form spontaneously and the protein-DNA complex dissociates. The interaction we characterize herein might increase the DNA binding affinity temporarily in DNA-bound c-Ets1. In v-Ets in which the C-terminal domain is mutated this interaction appears to lead to strong DNA binding affinity. Therefore, changes in v-Ets might contribute to the tumorigenic process by altering intramolecular interactions.