Table I. Random mutations on three key residues of Kch’s filter (G187, Y188 and G189) and their effect on the S331P GOF mutant phenotype.

	Filter sequence
	G187		Y188		G189
	Codon	A.A.	Codon	A.A.	Codon	A.A.
Wild type	GGC	G	TAT	Y	GGC	G
Mutations that suppress the GOF phenotype	TGC	C
	CAG	Q
			GGC	G
			ACT	T
			CGC	R
			ATA	I
			AAA	K
					CAA	Q
					TCC	S
					AGC	S
					GAC	D
					CTT	L
					TTC	F
					AGA	R
					AAT	N
					AGT	S
					TCA	S
					AAA	K
					TCC	S
					GCA	A
					GAG	E
Do not suppress			TTC	F
			TAT	Y
			TTC	F
			TAT	Y
			TTT	F