Models of the AtPum13 PUM-HD bound to RNA. Ribbon (A) and stick (B) models of the PUM-HD of AtPUM13 bound to the core nucleotides of Box 2 of the NRE1 (UUGUAUAU). (C) Sequence alignment of residues in helix 2 of repeats 1-8 that provide putative RNA contact sites on the concave surface of the PUM-HD. (D) Schematic diagram showing the protein:RNA contacts in the model of the AtPum13 PUM-HD. Legend details are described in Figure 5.