Chitin is mainly formed by the chitin synthase III complex (CSIII) in yeast cells. This complex is considered to be composed of the catalytic subunit Chs3 and the regulatory subunit Chs4, both of which are phosphoproteins and transported to the plasma membrane by different trafficking routes. During cytokinesis, Chs3 associates with Chs4 and other proteins at the septin ring, which results in an active CSIII complex. In this study, we focused on the role of Chs4 as a regulatory subunit of the CSIII complex. We analyzed the dynamic localization and interaction of Chs3 and Chs4 during cell division, and found that both proteins transiently co-localize and physically interact only during bud formation and later in a period during septum formation and cytokinesis. To identify unknown binding partners of Chs4, we conducted different screening approaches, which yielded several novel candidates of Chs4-binding proteins including the septin-associated kinase Gin4. Our further studies confirmed this interaction and provided first evidence that Chs4 phosphorylation is partially dependent on Gin4, which is required for proper localization of Chs4 at the bud neck.

中文翻译：

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Septin相关蛋白激酶Gin4影响Chs4的定位和磷酸化，Chs4是贝克酵母几丁质合酶III复合物的调节亚基。

几丁质主要由酵母细胞中的几丁质合酶III复合物（CSIII）形成。该复合物被认为由催化亚基Chs3和调节亚基Chs4组成，它们都是磷蛋白，并通过不同的运输途径转运至质膜。在胞质分裂过程中，Chs3与Seps环上的Chs4和其他蛋白缔合，从而形成活性CSIII复合物。在这项研究中，我们集中于Chs4作为CSIII复杂的调节亚基的作用。我们分析了Chs3和Chs4在细胞分裂过程中的动态定位和相互作用，发现这两种蛋白质仅在芽形成过程中以及在隔垫形成和胞质分裂期间的某个时间瞬时共定位并物理相互作用。为了识别Chs4的未知结合伴侣，我们进行了不同的筛选方法，产生了几种新的Chs4结合蛋白候选物，包括与Septin相关的激酶Gin4。我们的进一步研究证实了这种相互作用并提供了第一个证据，证明Chs4的磷酸化部分依赖于Gin4，这是Chs4在芽颈处正确定位所必需的。