(A) Structural organization of the human ABCA17P/ABCA3 gene locus on chromosome 16p13.3. Both genes are organized in head-to-head orientation on opposite strands and overlap at their 5' ends. Exons are represented by black (ABCA17P) and gray boxes (ABCA3), respectively, and numbered in 5' to 3' order. Numbers in parentheses refer to ABCA3 exons that share >70% sequence homology with the ABCA17P exons indicated. The yellow box highlights the alternative exon 1b of the ABCA17P gene. The green box represents a common CpG island at the 5' end of both genes. A metric scale bar is shown. (B) Comparison of the human and mouse ABCA17 – ABCA3 gene borders. Shown are the first two exons of both genes and arrows indicate the respective directions of transcription. Note that the human ABCA17P and ABCA3 genes share a 1.2 kb overlap (brown box), whereas the murine Abca17 and Abca3 orthologs are separated by a 1.0 kb intergene region (blue box). An arrow identifies the novel exon 1 of the murine Abca17 gene. A metric scale bare is shown at the bottom. (C) Synopsis of alternative ABCA17P transcripts identified in this study. Shown are 20 ABCA17P transcript variants which are generated by alternative splicing of exons 2, 3, 9, 10 and a segment of exon 11 (red box), respectively. Boxes represent exons; the alternative first exon 1b is depicted by a yellow box.