Complexity of the Mypt2 (PPP1R12B) locus. A: protein phosphatase 1 regulatory subunit 12B (PPP1R12B) locus hosts independent transcriptional start sites (TSS) for Mypt2 (982 aa), heart-specific M21 (hsM21) (208 aa), and smooth muscle M21 (smM21) (186 aa). The first exons and start codons (ATG) for each transcript are highlighted and color coded in this diagram that uses the human PPP1R12B as the template (red: Mypt2; blue: hsM21; green: smM21). The alternate stop codons (TAG) are also diagrammed. The region corresponding to the first exon of the mouse hsM21 is depicted by a gray box. Experimental evidence for independent transcriptional regulation (regions of histone 3 modification, DNase hypersensitivity, TF ChIP) is shown for the first exons of human Mypt2(B) hsM21 (C), and smM21 (E). SwitchGear predicted TSSs are depicted as red lines. The mammalian and vertebrate conservation is also shown. D: experimental evidence for transcriptional regulation of the first exon of mouse hsM21 and conservation are shown.