This protocol describes the electroporation of the BMH 81-17 mut S strain that is recommended for tranformation of the site directed mutagenesis of dsDNA (See Protocol on Site-Directed Mutagenesis on Double Stranded DNA). BMH 81-17 mut S are a mismatch repair defective (mut S) Escherichia coli strain. The probability that the two mutations will cosegregate during the first round of DNA replication is increased in this strain.