A RAPID METHOD FOR SITE-SPECIFIC MUTAGENESIS USING LARGER PLASMIDS AS TEMPLATES

To facilitate the introduction of specific point mutations in plasmids that are too large to be amplified efficiently by a single PCR, we have developed a method for site-directed mutagenesis by generating partial plasmid fragments, which introduces changes as simply as conventional techniques. Plasmids containing a fragment of the human immunodeficiency virus type-1 (HIV-1) envelope gene were subjected to PCR with four pairs of PCR primers for each desired point mutation. One primer in each of two of these four pairs contained the desired mutation. The four pairs of primers were designed so that four overlapping fragments were amplified from the plasmid template, two of which contained the mutation. These fragments were then reannealed and electroporated directly into Escherichia coli. The desired mutation was typically found in 66% to 83% of the resulting colonies. The technique is almost as simple as previous techniques, shows similar efficiency and is applicable to plasmids that would normally be too large for efficient site-specifc mutagenesis. The entire procedure, from PCR amplification to transfection into E. coli, can be completed in one day.