Three molecular changes have been identified in this allele. A 2 kb deletion encompasses exons 2 and 3 including the translation initiation sequence. An inversion exceeding 40 kb encompasses much of the coding region. An additional 0.5 kb sequence downstream of the inverted 40 kb has been duplicated and inserted in reverse orientation just upstream of this 40 kb inversion. Northern blots of adipose tissue extracts failed to detect mRNA from mice homozygous for this allele.