Table 1. Amino acid residues at which Cys substitutions inhibited PA activity by at least 100-fold.

Domain	Residues
1	I210, K225, T240, K245
2	S337, G342, W346, T357, I364, P379, T380, S382, T390, T393, K397, N399, Y411, I419, A420, N422, F427, S248, D451, D453, V455, N458
3	E515
4	I656, N657, I665, N682, D683, L687

The toxicity of the PA mutants was tested by two successive assays as described in the text.