Recent structures of the Runx1-CBF beta heterodimer bound to DNA brings to
six the number of characterized eukaryotic transcription factor families th
at use an immunoglobulin (Ig) fold to bind to DNA. Variation in the loop re
gions accounts for the diversity of DNA sequences recognized by Ig-fold pro
teins, but there are recurring themes in the interactions made by specific
loop regions and how these interactions are regulated.