Fig. 1. Synthesis of sphingolipids in yeast from endogenous and exogenous precursors. DHS and PHS can be internalized by cells and phosphorylated by the LCB4 and LCB5 gene products to give DHS-1P and PHS-1P. The phosphorylated sphingoid bases can be dephosphorylated by the LCB3 and YSR3 gene products. LCB1 encodes a subunit of serine palmitoyltransferase. The SUR2 gene product converts DHS into PHS. Synthesis of ceramides from DHS or PHS and C26 fatty acyl-CoA is inhibited by australifungin. Ceramides are used to synthesize the sphingolipids IPC (inositolphosphorylceramide), MIPC (mannosylated inositolphosphorylceramide) and M(IP)₂C (mannosylated di-inositolphosphorylceramide).