Fig. 4 Comparison of the structure of the solution structure of the Nab2 N-terminal domain with PWI folds seen in the solution structures of SRm160 (PDB accession code 1MP1) and the U4/U6 small nuclear ribonucleoprotein, Prp3 (PDB accession code 1X4Q). The arrangement of helices H1–H4 of the Nab2 N-terminal domain is similar to that of the PWI folds, although these do not contain an element analogous to helix H5.