Method: The following sense with cognate antisense (not shown) oligonucleotides (Integrated DNA Technologies, Coralville, IA) was used in the mutagenesis:
G118R, 5'-GTACATACAGACAATCGCAGCAATTTCACCAGTAC-3';
E138K, 5'-GGCGGGGATCAAGCAGAAATTTGGCATTCCCTA-3';
G140A, 5'-GGGGATCAAGCAGGAATTTGCCATTCCCTACAATC-3';
G140S, 5'-GGGGATCAAGCAGGAATTTAGCATTCCCTACAATC-3';
Y143R, 5'-GCAGGAATTTGGCATTCCCCGCAATCCCCAAAGTCAAGGA-3';
Q148H, 5'-CATTCCCTACAATCCCCAAAGTCATGGAGTAATAGAATCTA-3';
Q148K