Table 1. Intein Mutations and Surface Display Levels.

	amino acid
	21	33	50	51	74	105	107	110	112	114	117	118	124	129	144	158	160	164	168	190	191	fold increasea	statistical significanceb
wild-type	I	I	L	F	N	I	R	F	V	C	F	A	F	Y	H	D	R	A	S	I	T	1.0 ± 0.0
202–03					D					R					R	G						1.4 ± 0.1	**
202–08				L		V	C	S			L		L						G	T		1.8 ± 0.2	**
202–12		T	P						A		C											1.5 ± 0.3	*
202–13	T			S						G		T					Q					1.3 ± 0.2	NS
505–05	T									R										V		1.3 ± 0.1	**
505–11														C				P			M	1.7 ± 0.1	**

^aFold increase relative to the wild-type intein as fusions to 4–4–20, mean ± SD from three independent yeast transformants.

^bStatistical analysis was perfomed by an unpaired Student’s t-test, with double asterisks representing p < 0.01, single asterisks representing p < 0.05, and NS designating that differences are not significant (p > 0.05).