Structure and function of the PUF family protein Pumilio. The protein is crescent shaped, with 10 repeated α-helical segments, each consisting of about 40 amino acids. The 8 repeats in the middle (colored) are involved in mRNA binding. The 2 repeats on the ends (white) are important to Pumilio function, but do not directly participate in mRNA binding. Binding of a PUF family protein to the 3′UTR of an mRNA, as shown on the right, suppresses protein production either through interference with translation initiation by blocking assembly of translational factors or through promotion of mRNA degradation by recruiting RNA degradation enzymes. [Source: PDB ID 1M8Y.]