Replacement-like recombination induced by an integration vector with a murine homology flank at the immunoglobulin heavy-chain locus in mouse and rat hybridoma cells.
1994
Lang P. | Mocikat M.
Vectors for homologous recombination are commonly designed as replacement or integration constructs. Integration vectors were evaluated for the substitution of the immunoglobulin heavy-chain constant region by various human isotypes in mouse and rat hybridomas. It is known that under certain circumstances replacement vectors exhibit a lower target efficiency and can be incorporated by integration events. Conversely, it was shown that an integration vector can undergo a replacement event despite having free homologous adjacent DNA ends, which would be expected to initiate integration according to the double-strand break repair model. Moreover, in cases of replacement recombination the 5' crossover is not necessarily located within the homology region, thereby giving rise to a truncated gene product. Whether or not the replacement leads to such deletions is clearly dependent on the isotypes involved in the targeting reaction. The fact that the vector is correctly targeted to the heavy-chain locus, but that the homology region is not always the site of recombination, points to a novel recombination mechanism that may be specific for the immunoglobulin loci and that seems to be predominant even in the presence of the free homologous adjacent ends of an integration vector. Furthermore it is demonstrated that homologous recombination at the heavy-chain locus is also possible between sequences from different species. The implications of these findings for the production of chimeric antibodies are discussed.
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