Mucins may be the ugly ducklings of molecular biology. Their large size, repetitive nature, and unglamorous biological activities have not favored their study. However, integral membrane mucins have conserved intracellular C termini that may influence intracellular signaling. In a recent issue of Genes & Development, Cullen et al. show that the C terminus of membrane mucin-like Msb2 activates a CDC42/MAPK cascade to control filamentous growth of baker's yeast.