The L1L2_gt2 cassette was inserted at position 131580788 of Chromosome 4 upstream of the critical exon 2 (Build GRCm39). The cassette is composed of an FRT flanked lacZ/neomycin sequence followed by a loxP site. An additional loxP site is inserted downstream of the targeted exon 2 at position 131581364. Exon 2 is thus flanked by loxP sites. A null/knockout allele was created by flp and cre recombinase expression in mice carrying this allele to remove the lacZ sequence, neo selection cassette and the loxP-flanked exon 2. Further information on targeting strategies used for this and other IKMC alleles can be found at http://www.informatics.jax.org/mgihome/nomen/IKMC_schematics.shtml. Western blot analysis confirmed the absence of protein expression in homozygous mutant embryos. No lipoylated proteins could be detected in E9.5 homozygous embryos, consistent with complete loss of Mecr function in this line.