Crystal structure of a Pumilio homology domain

Puf proteins regulate translation and mRNA stability by binding sequences i n their target RNAs through the Pumilio homology domain (PUM-HD), which is characterized by eight tandem copies of a 36 amino acid motif, the PUM repe at. We have solved the structure of the PUM-HD from human Pumilio1 at 1.9 A ngstrom resolution. The structure reveals that the eight PUM repeats corres pond to eight copies of a single, repeated structural motif. The PUM repeat s pack together to form a right-handed superhelix that approximates a half doughnut. The distribution of side chains on the inner and outer faces of t his half doughnut suggests that the inner face of the PUM-HD binds RNA whil e the outer face interacts with proteins such as Nanos, Brain Tumor, and cy toplasmic polyadenylation element binding protein.