Figure 7. PUM repeats form three distinct classes of RNA-binding proteins.

Schematic drawings of the crystal structures of human PUM1 (left), yeast Nop9 (centre) and human Puf-A (right). PUM repeats at structural junctions in Nop9 and Puf-A are coloured yellow, and pseudorepeats at the N- and C termini are coloured grey. Puf-A comprises 11 PUM repeats, which are numbered N-R1 to N-R3 and C-R1 to C-R8 to indicate that its C-terminal repeats C-R1 to C-R8 form a curved structure similar to PUM1 (ref. ²¹).