A BAC (RP11-729B4) containing the human MS4A1 (hCD20) locus was modified by insertion of an IRES-cre/ERT2 (cre recombinase-mutated human estrogen receptor ligand-binding domain fusion) cassette into the 3' untranslated region of the gene. The modified BAC vector was used to generate a transgene that expresses a tamoxifen-inducible cre specifically in B cells. MS4A1 is also expressed from this allele. Line numbers are not available. (J:184524)