The HSV-1 thymidine kinase (TK) sequence was cloned into a construct containing the Krt15 (Krt1-15). The purified contruct was injected into fertilized (C57BL/6J x SJL/J)F2 oocytes. 6 founders were generated and lines 32 (2 copies of transgene) and 45 (3 copies) were used for further studies. (J:146740)