Consequences of heteromeric interactions among helix-loop-helix proteins.

DNA-binding proteins can be grouped according to the structural motifs that mediate their interactions with DNA. Thus far, several such motifs have been identified; these include the helix-turn-helix, the homeobox, the POU domain, the zinc finger, the basic-leucine zipper, and the basic-helix-loop-helix (1). In addition to providing a certain administrative convenience-there are presumably hundreds of DNA-binding proteins-such groupings can often provide insights into a protein’s function and regulation. This review will focus on HLH2 proteins and describe several examples that illustrate the relationships between structure and function within this protein family.