DETERMINANTS OF DNA-BINDING SPECIFICITY OF ETS-DOMAIN TRANSCRIPTION FACTORS

Several mechanisms are employed by members of transcription factor fam ilies to achieve sequence-specific DNA recognition. In this study, we have investigated how members of the ETS-domain transcription factor f amily achieve such specificity. We have used the ternary complex facto r (TCF) subfamily as an example. ERK2 mitogen-activated protein kinase stimulates serum response factor-dependent and autonomous DNA binding by the TCFs Elk-1 and SAP-1a. Phosphorylated Elk-1 and SAP-1a exhibit specificities of DNA binding similar to those of their isolated ETS d omains. The ETS domains of Elk-1 and SAP-1a and SAP-2 exhibit related but distinct DNA-binding specificities. A single residue, D-69 (Elk-1) or V-68 (SAP-1), has been identified as the critical determinant for the differential binding specificities of Elk-1 and SAP-1a, and an add itional residue, D-38 (Elk-1) or Q-37 (SAP-1), further modulates their DNA binding. Creation of mutations D38Q and D69V is sufficient to con fer SAP-1a DNA-binding specificity upon Elk-1 and thereby allow it to bind to a greater spectrum of sites. Molecular modelling indicates tha t these two residues (D-38 and D-69) are located away from the DNA-bin ding interface of Elk-1. Our data suggest a mechanism in which these r esidues modulate DNA binding by influencing the interaction of other r esidues with DNA.