Plant sucrose uptake transporters (SUTs) are H+/sucrose symporters, and OsSUT1 is a type II SUT. The OsSUT1(R188K) mutant was made that replaced lysine with arginine at position 188, altering a key residue in the transmembrane portion of the protein. R188H and R188M mutants did not localize to the membrane. 14C sucrose uptake by yeast expressing wildtype OsSUT1, the mutant, and an empty pDR196 gene vector was measured at pH 4.0 and 7.0, at 30˚C for 5 minutes each. The results are shown in the graph below:Based on the results obtained, OsSUT1 will localize and function properly at pH 4.0 as long as residue 188