Oligonucleotide-directed mutagenesis using M13-derived vectors: an efficient and general procedure for the production of point mutations in any fragment of DNA

This paper presents a versatile and efficient procedure for the construction of oligodeoxyribonucleotide directed site-specific mutations in DNA fragments cloned into M13 derived vectors. As an example, production of a transition mutation in a clone of the yeast MATal gene is described. The oligonucleotide is hybridized to the template DNA and covalently closed double stranded molecules are generated by extension of the oligonucleotide primer with E. coli DNA polymerase (large fragment) and ligation with T4 DNA ligase. The resulting double stranded closed circular DNA (CC-DNA) is separated from unligated and incompletely extended molecules by alkaline sucrose gradient centrifugation. This purification is essential for production of mutants at high efficiency. Competent E. coli JM101 cells are transformed with the CC-DNA fraction and single stranded DNA is isolated from individual plaques. The recombinants are screened for mutant molecules by 1) restriction endonuclease screening for the loss of the Hinf I site in the target region, and 2) by dot blot hybridization using the mutagenic oligonucleotide as probe. Double stranded DNA is isolated from the mutant and the production of the desired mutation is verified by DNA sequencing. Efficiency of mutant production is in the range of 10–45% and no precautions to prevent mismatch repair are required.