Effect of SV40 and MMTV promoters on intermolecular homologous recombination in rat cells.

The effect of SV40 and MMTV promoters on intermolecular homologous recombination between neomycin (neo) genes carrying deletions proximal and distal to the promoters has been examined in rat XC cells. One deleted neo gene linked to either promoter and the other deleted one without any promoter were co-transfected to cells so that the number of resulting G418-resistant colonies reflected the frequency at which the promoter-linked neo allele had been corrected by homologous recombination. We found that when the the distal deletion was placed under the SV40 promoter, it was corrected over 20-fold more frequently than the proximal. In contrast, when the MMTV promoter replaced the SV40 promoter, the distal deletion was corrected only 2-fold frequently compared with the proximal, and this result did not alter by activating the promoter with a glucocorticoid hormone dexamethasone. These results suggest that the preferential gene correction event observed with the SV40 promoter is attributed not to the transcriptional activity but to some specific sequence of the promoter.