A schematic representation of a signaling mucin is shown. Proteins that modify signaling mucins include O-glycosyltransferases, like GALNT6 and Pmt4, and proteases γ-secretase, Yps1, ADAM17/TACE, and MT1-MMP. Autocatalytic processing by the SEA domain is shown by a green arrow. The cytosolic domain is modified by ubiquitin (Ub), and phosphate (P) moieties. The cytosolic and transmembrane domains of MUC1 can translocate to the nucleus and associate with transcription factors to regulate gene expression. Modifiers of yeast mucin-like proteins are marked with an asterisk. Not all signaling mucins undergo all the modifications shown. The extracellular domain is not to scale and can be much larger than shown.