TABLE 1.

Expression of toxin by cysteine mutant clones

Clonea	Codon mutation	∼140-kDa proteinb
C26G1	C26G	+
C26G2	C26G	++
C26D	C26D	+
C113G1	C113G	+
C113G2	C113G	+
C113G3	C113G	+
C113V	C113V	+
C113*c	Frameshift at C113	−
C230G	C230G	(+)
C230D	C230D	(+)
C257S	C257S	+
C257I	C257I	+
C257Y	C257Y	+
C793G	C793G	+
C793Y	C793Y	+
C793*	Frameshift at C793	−
C905D1	C905D	+
C905D2	C905D	(+)
C905D3	C905D	+
C905Y	C905Y	+
C1159G1	C1159G	+
C1159G2	C1159G	++
C1165G1	C1165G	+
C1165G2	C1165G	+
C1165S	C1165S	+
C1165R	C1165R	+

^aThe independent isolation of identical mutant clones is indicated by subscript numbers 1 through 3. 

^bThe presence and intensity of a stained band on SDS-PAGE gels of cleared crude lysates corresponding to the expression of full-length PMT (∼140 kDa) from clone pTox2 was scored visually as follows: −, no ∼140-kDa band visible; (+), ∼50% less than pTox2; +, equivalent to pTox2; ++, ∼50% more than pTox2. 

^c*, premature stop codon generated by a frameshift mutation.