Table 2.

Classification of the mutants

Class	Mutation	# of mutants identified	β-galactosidase activity
I	dsbA and dsbB	27 dsbA and 20 dsbB	5–140 u.*
II	λ102 (malF-lacZ 102)	14	ND
III	ffs	25	0.2–8 u.†
	Gene X	1	4–5 u.
	Unmapped	2	8–11 u.

ND, not determined. 

^*Miller units. For reference, the wild type has β-galactosidase activity ranges from 0.05 to 0.08 units, and the dsbA or dsbB null mutants have β-galactosidase activity ranges from 120 to 180 units. 

^† β-galactosidase activities were quite variable. Most ffs mutants gave β-galactosidase activities between 1 and 8 units. ffs29, ffs69, and ffs91 used for subsequent studies repeatedly gave β-galactosidase activities above 1 unit.