TABLE 1.

Molecular masses of wild-type and mutant S12 proteins^a

Wild type or S12 mutation(s)	Phenotype	Observed mass (Da)	Predicted change in mol wt due to:		Observed change in mass vs wild type	D88 β-methylthiolation
			Amino acid change only	Amino acid change and loss of β-methylthiolation
Wild type	Strsb	14,519 ± 6				+
K87R	Strr	14,545 ± 1	+28	−19	+27	+
K87E	Strr	14,517 ± 4	−1	−48	−2	+
P90R	Strd	14,533 ± 5	+59	+12	+15	−
P90W	Strd	14,552 ± 2	+88	+41	+33	−
P90L	Strd	14,531 ± 2	+15	−32	+12	+
P90E	Strd	14,550 ± 4	+30	−17	+30	+
P90M	Strd	14,554 ± 9	+33	−14	+35	+
P90A	Strr	14,490 ± 6	−27	−74	−28	+
P90C	Strr	14,521 ± 2	+5	−42	+3	+
P90G	Strr	14,477 ± 6	−41	−88	−41	+
K42T P90R	Strr	14,506 ± 9	+31	−16	−13	−
K42T	Strr	14,490 ± 3	−28	−75	−28	+

^aThe theoretical (predicted) mass of wild-type S12 is 14,516 Da.

^bStr^s, streptomycin sensitivity.