Genomic and transcript structures of Slc35d3 in ash-Roswell and C3H/HeSnJ. Insertion of an IAP element (A) into exon 1 of the Slc35d3 gene (B) alters the 5′ terminal sequence of the Slc35d3 cDNA (C) to introduce a new IAP-derived ATG start site (bold and underlined in panel C) in the ash-Roswell mutant. This results in substitution of 21 new in-frame coding nucleotides (parentheses in panel C) for the 30 coding nucleotides (parentheses in D) found in control C3H DNA. The predicted result is the substitution of 7 new N-terminal amino acids in mutant Slc35d3 (see Figure 3E). IAP-derived sequences are in bold. A 7-bp duplication of endogenous gene sequences (GGCATCT), which is typical of IAP transpositions, is underlined. ATG start signals derived from the IAP and from the Slc35d3 gene are underlined. An additional 420 nucleotides at the 5′ end of the C3H/HeSnJ wild-type Slc35d3 cDNA are not listed.