A technique that can be used to make a protein that differs slightly in its structure from the protein that is normally produced (by an organism or cell). A single mutation (in the cell’s DNA) is caused by hybridizing the region in a codon to be mutated with a short, synthetic oligonucleotide. This causes the codon to code for a different specific amino acid in the protein gene product. Site-directed mutagenesis holds the potential to enable man to create modified (engineered) proteins that have desirable properties not currently available in the proteins produced by existing organisms.