Conservative Val47 residue of POU homeodomain: role in DNA recognition

Conservative Val47 residue, located in the third recognition helix of the Oct-2 POU domain, was alternately substituted with other 19 amino acids. Affinity and specificity of interaction with oct-site ATGCAAANGA and homeo-specific site ATAANGA were determined for all mutants. The wild type protein (with Val47) has maximal affinity and specificity in POU domain interaction with octamer sequence. However, V47I mutant showed stronger interaction with homeo-specific site. The highest specificity of interaction with homeo-site was recorded for V47S mutant. We conclude that only Val47 provides sequence-specific high-affinity binding of POU proteins with octamer targets other than the homeo-specific site. It is shown also that damages caused by point mutations may be at least partially compensated by participation in the oct-site recognition of both POUh and POUs domains.