A transgene expressing the murine H2-K b class I variant was derived from a 7.5-kb genomic clone. Dormant 150-bp loxP sites were inserted into the Hinc II site 5' of exon 1 and the Bam HI site in intron 3 of the construct. At the 3' end of the construct there is a 74-bp tail containing the 5' end of the HSV-1 thymidine kinase gene. (J:87648)