Mutagenesis is a fundamentally important DNA manipulation technique. It involves changing the base sequence of the DNA molecule, usually for the purposes of testing the effect of this change on gene or DNA function. Most site-directed mutagenesis is based on the PCR method, in which strand separation is accomplished by using a denaturing step to separate the complementary strands and in which efficient polymerization of the PCR primers is possible. In theory, the PCR method can be performed in the lab, but it requires considerable optimization, necessitates a staff skilled in both PCR and primer design. Often, the time and energy poured into in-lab PCR mutagenesis would be better spent elsewhere, such as on the lab's core creative work.