Cellular localization of Sun4p and its interaction with proteins in the yeast birth scar.

Yeast harbor several proteins with predicted glucanase activity that are potentially involved in cell wall remodeling during different processes, including mitosis. Here, we showed that 2 of these putative glucanases, Sun4p and Dse2p, co-localize to the yeast birth scar, dependently on presence of the third glucanase, Egt2p. The absence of these glucanases results in inefficient mother-daughter cell separation. The Sun4p, Dse2p and Egt2p localize to the daughter side of the bud neck, possibly forming a complex, and are involved in the separation of the virgin daughter from the mother cell during mitosis. The formation of properly assembled birth scars that delimitate cell wall area restricted in the next budding is dependent on the presence of Aim44p and its transcriptional regulator, Swi5p. AIM44 or SWI5 deletion caused the "budding within the birth scar" phenotype, together with altered localization of the birth scar proteins Sun4p and Dse2p, indicating the impairment of birth scar protein complexes.