FIG. 3.

Sites of point mutations. Letters outlined in black indicate sites of mutations. The encoded amino acids were unchanged by these mutations. lacZwt, wild-type lacZ. (B) β-Galactosidase activities in Miller units. Cultures were preincubated at 37°C for 1 h and then shifted to 42 or 32°C after addition of 1 mM isopropyl-β-d-thiogalactopyranoside. After 3 h, β-galactosidase activities were measured. Values presented are averages of results from three samples.