Table 1.

Oligonucleotide cassettes for the construction of pfDHFR mutants

Residue no.	Restriction site	Length of oligonucleotide cassette,* bases	Mutation (codon)
16	NdeI–SacII	115/111	Ala (GCA) to Val (GTA)
51	SacII–XbaI	42/48	Asn (AAC) to Ile (ATC)
59	XbaI–SnaBI	36/32	Cys (TGC) to Arg (CGC)
108	PstI–ClaI	35/41	Ser (TCG) to Asn (AAC)
			Ser (TCG) to Thr (ACC)
164	BglII–XhoI	67/67	Ile (ATC) to Leu (CTC)

^*Except for the indicated codon change, oligonucleotide cassettes had the same sequences as in the synthetic gene (19).