Zip code binding proteins are mRNA localisation proteins that bind to zip code sequences on mRNAs. This allows the localisation of translation to specific regions of the cell, which can be beneficial in body patterning by HOX genes and anterior/posterior axis formation.
The zip code sequence is typically found in the 3’ UTR, and is not translated into the final protein product.
In Saccharomyces cerevisiae, actin cables are used to localise ASH1 to the daughter cell, converting the parental cell’s mating type during budding. The zip code sequence of ASH1 binds to the zip code binding proteins, which are then attached to the actin cables, allowing the transcript to be localised to the daughter cell. This enables the parental cell to switch from mating type $$a$$ or $$\alpha$$ to the opposite, with the daughter cell being the same as the parental cell prior to the division.