Exon 1 through part of intron 2 was replaced with the corresponding sequence from C57BL/6 mice. Although the ES cells used to create this allele were (129S1/SvImJ x NOD/ShiLtJ)F1 the targeting event was mapped to the NOD allele. The floxed neo cassette downstream of the inserted sequence was removed by transient cre expression in ES cells. (J:150823)