Double partial phylogenetic profiling (DPPP) using the GTP-binding protein HydF (GI:113971588) as query. For the query protein (red), the curve rises monotonically, because it measures the correlation of the list of species it generates to itself. Among all proteins other than the query, the peak score for any protein occurs (for HydE, GI:113971587,) where the query protein BLAST hits list depth is about 210. DPPP scores are shown for query protein depths 10 to 930, sampled every tenth hit, for the ten proteins that scored the best at the depth 210. The curves for HydE (GI:113971587, olive), HydG (GI:113971585, green), and the hydrogenase large (GI:113971582, blue) and small (GI:113971583, purple) subunits all peak at this query protein depth, which largely exhausts the list of species that carry the [FeFe] hydrogenase maturation system (see text and Table 3 for details). Proteins unrelated to [FeFe] hydrogenase maturation are shown in gray.