Figure 3. Representation of the two-hybrid septin-septin results in the light of the format of the trimer/hexamer SEPT7/SEPT6/SEPT2 – SEPT2/SEPT6/SEPT7 [18].

Assuming that members of the same group may serve as substitutes [6] and taking into account the structural arrangement found for the crystal of the trimer/hexamer SEPT 7/6/2, interesting observations can be made. The bait septins employed in the two-hybrid system are given on the left. In green in the schematic figure the preferentially found prey septins are indicated and assigned to likely positions in the hexamer scheme. The three dimensional column diagrams on the right refer to Fig. 2. The data that differ significantly from a random distribution have been circled to indicate the experimental basis on which each structural arrangement (monomer interfaces) is based. From top to bottom: (a) is based on the following statistical comparison: group 6 vs. group 2 (no random distribution: p< 0.001), group 6 vs. group 3/9 (p<0.001), group 6 vs. 7 (p<0.001). (b): group 2 vs. group 6 (p<0.001), (c): group 3/9 vs. group 6 (p<0.001), group 7 vs. group 9/3 (p<0.001), (d): group 7 vs. group 6 (p<0.001), group 7 vs. group 9/3 (p<0.001). None of the septins fished members of its own family, except group two members (b). The group pairings with statistically significant clone distributions were indicated at the right side of the figure (e.g. 6×7, 3/9×6 etc.). By comparison of the letters color codes it can be seen that all of these group pairs were reciprocal. For example bait septin 6 group fished group 2 septins (a) and vice versa (b) (p <0.001). As initially proposed by Kinoshita there may be substitutions among different members of the same septin group. The sequence of listed septins from left to right reflects a descending order of frequency of clones with septins that were found to interact (e.g. for SEPT6 bait: 9,3,7 and 5,1,4,2).