An ! helix inserts into a major

groove of operator DNA
One part of the protein, an ! helix (the
sequence-reading or recognition helix) is inserted
into the major groove of DNA. Here the
sequence Q-Q-Q-S-T (glutamine Q, serine S,
threonine T) in the recognition sequence of the
bacteriophage 434 repressor bonds with
specific bases in a major groove of operator
DNA.