Fig. 4. Evolution of lineage-specific mucins from proteins that are rich in proline (mucinization).

Three examples of lineage-specific mucinization events are shown. The branches in the phylogeny where mucinization likely occurred are indicated by red dots. The homologous regions are shown with lines, and BLAST e values are provided. The proposed mechanism of how a nonmucin precursor protein (top) gives rise to its orthologous mucin protein (bottom) is schematically shown for the three examples, i.e., rhinoceros (rhino), cat, and cow (indicated by stars on the phylogeny). Exonic repeats are indicated by small boxes. Number of repeats and number of nucleotides per repeat are indicated below the designated repeat sections in bold. Blue color intensity indicates approximate PTS richness.