Comparison of amino acid conservation between Toc64TPRs and the HopTPRs and Sec72. In (a–c), the homology model of Sec72TPR of Saccharomyces cerevisiae is shown. (a) represents the view into the chaperone-binding pocket, and in (b), the model is rotated by 180° around the y axis. From a probability matrix representing for each amino acid the probability to occur in Hsp90- and of Hsp70-binding TPR domains (values in the range [−1.0, 1.0]; values <0 denote Hsp70, and values >0 an Hsp90 preference), the value for the amino acid with the highest frequency in a multiple sequence alignment of Sec72TPR was extracted for every position. Subsequently, the structure is colored by the significance of a residue to define an Hsp90- or Hsp70-binding TPR domain ([−1,−0.5] blue, [−0.5,−0.1] cyan, [−0.1, 0.1] yellow, [0.1, 0.4] orange, [0.4, 1] red). The procedure is described in more detail in supplementary figure 5 (Supplementary Material online). In (c), the same view as in (a) is shown, but only amino acids involved in chaperone binding (Scheufler et al. 2000) are colored. Molecular graphics created with YASARA (www.yasara.org) and PovRay (www.povray.org).