A new pattern for helix-turn-helix recognition revealed by PU.1-domain-DNA complex

THE Ets family of transcription factors, of which there are now about 35 members1,2, regulate gene expression during growth and development. They share a conserved domain of around 85 amino acids3 which binds as a monomer to the DNA sequence 5'-C/ AGGAA/T-3'. We have determined theocrystal structure of an ETS domain complexed with DNA, at 2.3-Å resolution. The domain is similar to α+β (winged) 'helix–turn–helix' proteins and interacts with a ten-base-pair region of duplex DNA which takes up a uniform curve of 8°. The domain contacts the DNA by a novel loop–helix–loop architecture. Four of the amino acids that directly interact with the DNA are highly conserved: two arginines from the recognition helix lying in the major groove, one lysine from the 'wing' that binds upstream of the core GGAA sequence, and another lysine, from the 'turn' of the 'helix–turn–helix' motif, which binds downstream and on the opposite strand.