TABLE 2.

Second-site suppressor mutations

Specificity of suppression	Second-site suppressor	Corresponding codon change	Location in PAS domain	Frequency of amino acid substitution in other Aer-like PAS domainsa
Nonspecific	S28G	AGC → GGC	PAS core, Bβ	G conserved at this position in many other PAS domains
	A65V	GCG → GTG	EF loop	A and V occur in other PAS domains, but this is not a conserved position in the PAS alignment
	A99V	GCG → GTG	β-Scaffold, Hβ	Type of amino acid not conserved at this position
Site specific	N34D	AAT → GAT	PAS core, Cα	N is conserved at this position in many other PAS domains; no PAS domains contain D at this position

^aAlignment from reference 38.