Efficient nonhomologous and homologous recombination in scid cells.

The severe combined immunodeficiency (scid) mutation affects both coding joint formation during immunoglobulin and T-cell receptor V(D)J recombination and double-strand break repair. We analyzed scid cells for their ability to undergo other types of DNA end joining: nonhomologous and homologous recombination. Using plasmid constructs carrying antibiotic resistance genes, we observed that the efficiency of nonhomologous integration in scid cells was equal to that in wildtype cell lines. In addition, there was no obvious difference in the fidelity of the integration and in the expression of the resistance genes. Moreover, scid cells were able to carry out homologous recombination of extrachromosomal substrates just as well as wildtype cells. These results suggest a mechanistic difference between nonhomologous integration and homologous recombination on the one hand and V(D)J recombination and double-strand break repair on the other.