| Summary: | <p>Abstract</p> <p>Background</p> <p>In <it>S. cerevisiae </it>the β-1,4-linked N-acetylglucosamine polymer, chitin, is synthesized by a family of 3 specialized but interacting chitin synthases encoded by <it>CHS1</it>, <it>CHS2 </it>and <it>CHS3</it>. Chs2p makes chitin in the primary septum, while Chs3p makes chitin in the lateral cell wall and in the bud neck, and can partially compensate for the lack of Chs2p. Chs3p requires a pathway of Bni4p, Chs4p, Chs5p, Chs6p and Chs7p for its localization and activity. Chs1p is thought to have a septum repair function after cell separation. To further explore interactions in the chitin synthase family and to find processes buffering chitin synthesis, we compiled a genetic interaction network of genes showing synthetic interactions with <it>CHS1</it>, <it>CHS3 </it>and genes involved in Chs3p localization and function and made a phenotypic analysis of their mutants.</p> <p>Results</p> <p>Using deletion mutants in <it>CHS1</it>, <it>CHS3</it>, <it>CHS4</it>, <it>CHS5</it>, <it>CHS6</it>, <it>CHS7 </it>and <it>BNI4 </it>in a synthetic genetic array analysis we assembled a network of 316 interactions among 163 genes. The interaction network with <it>CHS3</it>, <it>CHS4</it>, <it>CHS5</it>, <it>CHS6</it>, <it>CHS7 </it>or <it>BNI4 </it>forms a dense neighborhood, with many genes functioning in cell wall assembly or polarized secretion. Chitin levels were altered in 54 of the mutants in individually deleted genes, indicating a functional relationship between them and chitin synthesis. 32 of these mutants triggered the chitin stress response, with elevated chitin levels and a dependence on <it>CHS3</it>. A large fraction of the <it>CHS1</it>-interaction set was distinct from that of the <it>CHS3 </it>network, indicating broad roles for Chs1p in buffering both Chs2p function and more global cell wall robustness.</p> <p>Conclusion</p> <p>Based on their interaction patterns and chitin levels we group interacting mutants into functional categories. Genes interacting with <it>CHS3 </it>are involved in the amelioration of cell wall defects and in septum or bud neck chitin synthesis, and we newly assign a number of genes to these functions. Our genetic analysis of genes not interacting with <it>CHS3 </it>indicate expanded roles for Chs4p, Chs5p and Chs6p in secretory protein trafficking and of Bni4p in bud neck organization.</p>
|
|---|