The human SHBG gene locus on chromosome 17p13.1 and its transcriptional expression. Top: Exon structures of the SHBG gene and its neighboring genes are given as vertical lines. Transcriptional polarity is denoted by arrows. The polarity (designated by arrows) of the SHBG gene is opposite that of the SAT2 and FXR2 genes. SHBG upstream exon 1T abuts the SAT2 gene, and exon 1N is located within intron 1 of the FXR2 gene. Note the close proximity of the p53 gene. Bottom: An expanded structure of the human SHBG gene, showing the three SHBG gene promoters, PL, PT, and PN, the three first exons, 1L, 1T, and 1N, and downstream exons 2–8. Numbers refer to relative positions along chromosome 17. Below is a representation of the structures of the 19 known human SHBG gene transcripts (boxes represent exons). Transcript structures are given on the right. Those representing the two major transcripts (SHBG/ABP and SHBG-T) and two minor transcripts (1L-8 lacking exon 7, and 1T-8) from prior reports are underlined. Alternative splicing of exon 4 from 1L-8 and 1T-8 transcripts was not specifically detected; these putative transcripts are presented in parentheses.