The highly conserved DNA-binding domains of A-, B- and c-Myb differ with respect to DNA-binding, phosphorylation and redox properties

In the Myb family, as in other families of transcription factors sharing si milar DNA-binding domains (DBDs), diversity of function is believed to rely mainly on the less conserved parts of the proteins and on their distinct p atterns of expression. However, small conserved differences between DBDs of individual members could play a role in fine-tuning their function. We hav e compared the highly conserved DBDs of the three vertebrate Myb proteins ( A-, B- and c-Myb) and found distinct functional differences. While A- and c -Myb behaved virtually identically in a variety of DNA-binding assays, B-My b formed complexes of comparatively lower stability, rapidly dissociating u nder competitive conditions and showing less tolerance to binding site vari ations. The three protein domains also differed as substrates for protein k inases. Whereas PKA in theory should target the DBI)s of A- and c-Myb, but not B-Myb, only c-Myb was phosphorylated by PKA. CK2 phosphorylated all thr ee proteins, although on different sites in the N-terminal region. Finally, B-Myb was remarkably sensitive to cysteine-directed oxidation compared to the other Myb proteins. Our data suggest that the small differences that ha ve evolved between individual Myb family members lead to clear differences in DBD properties even if their sequence recognition remains the same.