So proteins can be modified at a single amino acid by using this process we call side directive mutagenesis. Now, to demonstrate how this process works, let's suppose we have a protein and we want to change an amino acid glutamate to the amino acid aspartate in that protein. How exactly can we do this? Well, we need two things. Number one, we need that double stranded DNA molecule that contains the gene that encodes for that protein in the first place, the correct sequence of nucleotides. And we also actually need to know the sequence of nucleotides around that area that we want to modify.