The Ets family of genes encode nuclear proteins that activate transcription by binding to a specific purine-rich (GGAA) ets binding sequence (EBS) present in promoters/enhancers of various genes. It has previously been shown that over-expression of ets1 via transfection of ets1 expression vectors into NIH3T3 cells induced the expression of the endogenous Ets1 gene. In this study, it is shown that the autoregulation occurs as a result of the ets1 protein binding to the EBS-core located in its own promoter. Ets binding sites in the IL-4, G-CSF (granulocyte colony stimulating factor), as well as the 2'5' OAS (oligoadenylate synthetase) promoter, have also been identified by binding with Ets1 and Ets2 proteins using the electrophoretic mobility shift assays. Interestingly, it has been found that the EBS containing T nucleotides on either side of the GGAA does not bind Ets1 or Ets2 proteins. These findings demonstrate that the sequences surrounding the purine core have a profound influence on the binding of Ets proteins. Additionally, the ets1 DNA binding activity was found to be localized within a region of 143 amino acids located at the carboxy terminus of the ets1 protein. By comparing the amino acids within the tryptophan repeats of myb and Ets, it was found that the myb first repeat is 35% identical to the Ets repeat. In addition to the highly conserved tryptophan residues, other amino acids are also conserved between myb and Ets family proteins. The most consistent conservations are two leucine residues present at positions 7 and 8 downstream of the first tryptophan; a phenylalanine and lysine at positions 8 and 9; a valine at position 16 downstream of the second tryptophan; and arginine or leucine residue adjacent to the third tryptophan. Therefore, it may be that these highly-conserved hydrophobic and basic residues that are conserved between Ets family members and myb are important for DNA binding of these proteins.