Targeted correction of a major histocompatibility class II E alpha gene by DNA microinjected into mouse eggs.

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Abstract
DNA molecules containing the 5'' end of a functional major histocompatibility class II E.alpha. gene were injected into mouse eggs bearing E.alpha. genes with 630-base-pair (bp) deletions encompassing the promoter and first exon. The deletion was corrected by homologous recombination in 1 of about 500 transgenic mice that incorporated the injected DNA. The corrected E.alpha. gene was transmitted to progeny, which were bred to homozygosity. Southern blot analysis, polymerase chain reaction amplification of the DNA spanning the deletion, and sequence analysis revealed that the corrected allele resembles the wild-type E.alpha. gene. At sites of single-base-pair polymorphisms, there was apparently random conversion to either the donor or recipient sequence. In addition, many point mutations were introduced. mRNAs were produced from the corrected allele in a tissue-specific manner, but their sizes were different from the wild-type allele, and they did not produce detectable E.alpha. protein. This experiment demonstrates the feasibility of targeting foreign DNA to a gene that is completely inactive in fertilized mouse eggs.