The spatial landmark protein Bud8 plays a crucial role in bipolar budding in the budding yeast Saccharomyces cerevisiae. The unconventional yeast Yarrowia lipolytica can also bud in a bipolar pattern, but is evolutionarily distant from S. cerevisiae. It encodes the protein YALI0F12738p, which shares the highest amino acid sequence homology with S. cerevisiae Bud8, sharing a conserved transmembrane domain at the C-terminus. Therefore, we named it YlBud8. Deletion of YlBud8 in Y. lipolytica causes cellular separation defects, resulting in budded cells remaining linked with one another as cell chains or multiple buds from a single cell, which suggests that YlBud8 may play an important role in cell separation, which is distinct from the function of Bud8 in S. cerevisiae. We also show that the YlBud8-GFP fusion protein is located at the cell membrane and enriched in the bud cortex, which would be consistent with a role in the regulation of cell separation. The coiled-coil domain at the N-terminus of YlBud8 is important to the correct localization and function of YlBud8, as truncated proteins that do not contain the coiled-coil domain cannot rescue the defects observed in Ylbud8Δ. This finding suggests that a new signaling pathway controlled by YlBud8 via regulation of cell separation may exist in Y. lipolytica.
Keywords: YlBud8; cell polarity; cell separation; coiled-coil.