Fig. 3. Stereo diagram of a model of a putative LeuRSTT-tRNAleu editing complex obtained by superimposition of LeuRSTT on the IleRSSA-tRNAile editing complex (Silvian et al., 1999). The model tRNA used here is that of tRNAtyr with a long variable arm (S.Cusack, A.Yaremchuk and M.Tukalo, unpublished results). Its position has been manually adjusted to avoid steric clashes with the enzyme, notably with the ZN-1 domain, which is much closer to the active site in LeuRSTT than in the IleRSSA-tRNAile complex. The anticodon binding domain is in red, the editing domain in cyan. The model shows that the leucyl-specific domain (orange) could interact with the base of the acceptor stem and core of the tRNA. The long variable arm of the tRNA (green) points away from the enzyme and towards the viewer. This is consistent with it not being an important identity element, although it is possible that the disordered C-terminal domain of the enzyme makes some contact with this part of the tRNA. Given the flexibility of the various modules of the enzyme and of the tRNA itself, the aim of this figure is to give the general disposition of the various elements rather than to be an accurate model.