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. <i>AIM44</i> or <i>SWI5</i> 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.

酵母中存在多种具有预测葡聚糖酶（glucanase）活性的蛋白质，它们可能参与包括有丝分裂在内的多种过程中的细胞壁重塑。本研究证实，其中两种推定葡聚糖酶Sun4p与Dse2p可共定位于酵母出芽痕（birth scar），且该定位依赖于第三种葡聚糖酶Egt2p的存在。上述三种葡聚糖酶的缺失会导致母子细胞分离效率低下。Sun4p、Dse2p与Egt2p定位于芽颈的子细胞侧，可能形成复合物，并参与有丝分裂过程中新生子细胞与母细胞的分离。正确组装的出芽痕可划定下次出芽时受限制的细胞壁区域，这一过程依赖于Aim44p及其转录调控因子Swi5p。<i>AIM44</i>或<i>SWI5</i>基因的缺失会引发“出芽痕内出芽”表型，并伴随出芽痕蛋白Sun4p与Dse2p的定位异常，表明出芽痕蛋白复合物的功能受到损伤。