An ~120 kb mouse bacterial artificial chromosome (BAC) containing the entire mouse kallikrein related-peptidase 8 (Klk8; also called Prss19 or neuropsin) locus, and ~50 kb of upstream and ~70 kb of downstream sequences, was modified by targeting a human codon-optimized tetracycline-regulated transactivator gene (tTA or htTA or "Tet-Off") into the first exon upstream of the Prss19 translation initiation site. The resulting modified BAC was microinjected into (C57BL/6;DBA)F2 embryos. Founder mice were bred to C57BL/6J inbred mice to establish founder line S. (J:108340, J:151755)