TABLE I.

Summary of Mutant Behavior

	Residue at		Transport function
Protein	203	460	Leak	Cotransport	Surface expression
WT	A	S	+	+	+
Single	C	S	+	+	+
Double	C	C	+	+	+
	C	A	+	+	+
	C	L	+	+	+
	C	E	−	−	−
	C	R	+	−	+
Single	A	C	+	+	+
Double	S	C	+	+	+
	L	C	−	−	+
	R	C	−	−	+
	E	C	−	−	+

Summary of properties of mutants compared to the WT NaPi-IIa protein. Bold letters indicate the novel residue substituted at indicated site, using the single letter amino acid code. Symbols: +, detectable; −, undetectable.