Improvement in the visual discrimination of recombinant clones by size reduction of non-recombinant colonies

A flexible approach circumventing cloning problems related to incomplete vector double digest is described. DNA methyltransferase gene insertion into MCS of commonly used expression vectors facilitates identification of both: i) the correct linear fragment in agarose gels due to the dilator effect, and ii) recombinant colonies by size and opacity differences resulting from methyltransferase toxicity.