The effect of residue location on transposition rate, in the two regions of the protein (median, box: 25–75%, whiskers: 10–90%). (a) In the HTH-region, mutants of sectors, conserved or buried residues are not significantly different from the remaining mutants (P > 0.05 for all comparisons, Mann-Whitney U-tests). (b) In the DDE domain the differences are highly significant (P < 0.05 for all comparisons, Mann-Whitney U-tests), even after correcting for the different effects of free energy of folding (c). Note that in the DDE domain 50% of mutants of “other” residues are characterized with higher activity than the wild type SB.