Oligonucleotides used in this study Uppercase letters indicate identity to wild-type sequence. Oligonucleotides 784 and 786 contain a codon 252 mutation (GATAsp to GCTAla) and a silent mutation at codon 248 (TCASer to TCTSer) that creates a diagnostic DraI site. Oligonucleotides 783, 785, 798, and 799 contain a mutation at codon 255 (GAAGlu to GCGAla) that creates MluI and AflIII sites. Oligonucleotide 781 contains a BamHI site. Oligonucleotide 782 contains a SpeI site. Oligonucleotides 479 and 480 contain a BamHI site.