PA phosphatase activity of Pah1p is required for efficient formation of lipid droplets. (A) Diagram of Pah1p primary structure (modified from Han et al., 2007). NLIP, N-terminal lipin homology domain; HAD, haloacid dehalogenase-like domain. (B) The pah1Δ strain expressing the indicated PAH1 alleles on a pRS313 vector. The ER marker CFP-HDEL was expressed on a plasmid and driven by the PGK1 promoter. Lipid droplets were stained with BODIPY. Cells were observed in SD medium. Bar, 5 µm. (C) Droplet number per cell in strains shown in B. Error bars represent SEM based on three fields (∼50 cells per field) from three independent experiments. WT, wild type.