Palmitoylation of the fission yeast protein Isp3 is essential for the formation of the outermost layer of the spore wall

Abstract

Fission yeast spores possess strong resistance to environmental stresses, largely due to the outermost proteinaceous "Isp3 layer," which comprises Isp3 protein. Isp3 is palmitoylated, and its localization to the spore periphery is impaired in mutants lacking palmitoyltransferase; however, the precise role of Isp3 palmitoylation remains unclear. Here, we found that Isp3-GFP was expressed at wild-type levels in forming spores in mug142∆ cells lacking the palmitoyltransferase catalytic unit; thus, lack of palmitoylation did not reduce Isp3 protein stability. Next, we identified cysteine 7 as the key palmitoylation site essential for Isp3 localization to the spore periphery. Electron microscopy revealed that the Isp3 fibrillar layer was absent in both mug142Δ and isp3-C7S spores. Additionally, the isp3-C7S spores displayed increased sensitivity to alcohol stress, similar to isp3∆ spores. Collectively, these results demonstrate that palmitoylation of Isp3 is essential for the relocation of Isp3 to the spore surface and the assembly of the Isp3 layer.

Keywords: cell wall; palmitoylation; spore; yeast.