A structure for Utr-SR1-SR2 modeled from the Utr-SR1 crystal structure and a homology model for Utr-SR2.

<p>Ribbon representation of the hybrid Utr-SR1-SR2 model containing the experimentally determined Utr-SR1-L structure combined with an I-TASSER predicted model for Utr-SR2 superposed on the overlapping region (yellow). SR1 is colour coded A helix (dark blue), B helix (green), C helix (red), extended Utr-SR1-L region (yellow). SR2 is colour-coded helix A (mid-blue), helix B (green), helix C (brown). The orientation of the SR1 domain is approximately equivalent to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0040066#pone-0040066-g001" target="_blank">figure 1</a>. The close up view of the linker regions shows the heptad repeat phasing of L427 and L430 from Utr-SR1-L at the ‘a’ and ‘d’ heptad positions of helix A’ of SR2 forming coiled-coil interactions with the Utr-SR2 domain.