THE ETS-DOMAIN TRANSCRIPTION FACTORS ELK-1 AND SAP-1 EXHIBIT DIFFERENTIAL DNA-BINDING SPECIFICITIES

The ETS DNA-binding domain is conserved amongst many eukaryotic transcription factors. ETS-domains bind differentially to specific DNA sites containing a central GGA trinucleotide motif. The nucleotides flanking this motif define the binding specificity of individual proteins. In this study we have investigated binding specificity of the ETS-domains from two members of the ternary complex factor (TCF) subfamily Elk-1 and SAP-1. The ETS DNA-binding domains of Elk-1 (Elk-93) and SAP-1 (SAP-92) select similar sites from random pools of double stranded oligonucleotides based on the consensus sequence ACCGGAAGTR. However, SAP-92 shows a more relaxed binding site selectivity and binds efficiently to a greater spectrum of sites than does Elk-93. This more relaxed DNA binding site selectivity is most pronounced in nucleotides located on the 3' side of the GGA motif. This differential DMA-binding specificity is also exhibited by longer TCF derivatives and, indeed by the full-length proteins. Our results suggest that the range of potential on vitro target sites for SAP-1 is likely to be greater than far Elk-1. We discuss our results in relation to other similar studies carried out with more divergent ETS-domains.