The allele was generated by Cre-mediated deletion of 890kb genomic sequence of the lox71/loxP-flanked Igh region in Ightm4Mbu. The frt flanked Pgk1 promoter region was removed by Flpe recombinase in Ightm4.1Mbu. The allele contains only a promoterless blasticidin resistance gene at the deletion point. (J:341427)