Figure 1. APA leads to shorter 3′UTRs.
(A) Northern blots of human cell lines and tissues, successively stripped and reprobed for the indicated mRNAs. Groupings include sarcoma cell lines (brown), normal lung tissue, cultured human bronchial epithelial cells (NHBE) and immortalized lung epithelial cell line (Beas-2B, light green), lung cancer cell lines (dark green), normal colon tissue (light blue), colon cancer cell lines (dark blue), normal breast tissue and immortalized breast epithelial cell lines (orange), breast cancer cell lines (red), and other cell lines (grey), which were immortalized fibroblasts (HF) and an embryonic kidney cell line (HEK293). GAPDH expression served as loading control. Migration of markers with lengths indicated (kb) is shown at the right.
(B) Schematic illustration of mRNAs with alternative isoforms due to APA. Grey boxes show protein coding region; black line represents untranslated regions, and AAAAAA represents the poly(A) tail. Shown are functional APA signals identified by 3′ RACE, with signals conserved at the orthologous position in four genomes (human, mouse, rat, dog) in dark blue, and more poorly conserved signals in light blue. Brackets indicate closely spaced signals. Also shown are negative regulatory elements identified in the 3′UTRs, including AU-rich elements (ARE, green), let-7 sites (purple), and sites to the other widely expressed miRNA with the most sites in that 3′UTR (red).