V(D)J recombination is not activated by demethylation of the kappa locus

V(D)J recombination is thought to be regulated by changes in the accessibil ity of target sites, such as modulation of methylation. To test whether dem ethylation of the kappa locus can activate recombination, we generated two recombinationally active B cell lines in which the gene for maintenance of genomic DNA methylation, Dnmt1, was flanked with loxP sites. Transduction w ith a retrovirus expressing both the cre recombinase and green fluorescent protein allowed us to purify recombinationally active cells devoid of methy lation. Loss of methylation of the kappa locus was not sufficient to activa te recombination. although transcription was activated in one line. It appe ars that demethylation of the kappa locus is not the rate-limiting step for altering accessibility and thus regulated demethylation does not generate specificity of recombination.