A number of methods for generating random mutations in specific proteins were later developed to screen for mutants with interesting or improved properties. These methods may involve the use of doped nucleotides in oligonucleotides synthesis, or conducting a PCR reaction in conditions that enhance misincorporation of nucleotides (error-prone PCR), for example by reducing the fidelity of replication or using nucleotide analogues.[4] A variation of this method for integrating non-biased mutations in a gene is the Sequence Saturation Mutagenesis.[5] PCR products which contain mutation(s) are then cloned into an expression vector and the mutant proteins produced can then be characterised.