Fig. 1: An A. thaliana mutant, mag3, is defective in protein transport from the ER.

a Immunoblots of dry seeds of mag3 mutant alleles and their respective wild types with specific antibodies against major storage proteins; anti-12S globulin (anti-12S) and anti-2S albumin (anti-2S). Note that the mag3 seeds accumulated the precursors, pro12S globulin (p12S) and pro2S albumin (p2S), whereas wild-type seeds did not. tno1 is a mag3 mutant allele. b The identified MAG3 gene (AT1G24460) and the mutation sites of mag3 alleles. The MAG3 gene consists of eight exons (gray boxes) and seven introns (solid lines). The T-DNA insertions in six mag3 mutant alleles including tno1 are shown. MAG3 encodes a 198-kD protein composed of multiple coiled-coil regions (green) and a transmembrane domain at the C-terminus (orange). Anti-MAG3 antibodies were raised against the N-terminal region (amino acids 1–497) of the protein. c Immunoblots of 10-day-old seedlings of mag3 mutant alleles and their respective wild types with specific antibodies against MAG3 (anti-MAG3) and tubulin (anti-TUB). Arrowheads indicate truncated MAG3 proteins, while asterisks denote nonspecific bands. d Electron micrographs of the seed cells of the wild type (Ws-2) and mag3-1, showing that mag3 abnormally develop structures with electron-dense cores (circled). PSV, protein storage vacuole; CW, cell wall. See also Supplementary Fig. 1b for mag3-5. e Immunoelectron micrographs of the seed cells of mag3-1 with anti-12S and anti-2S conjugated with 15-nm nanogold particles, showing that the abnormal structures consist of electron-dense cores with 2S albumin and the matrix with 12S globulin. Enlarged images of boxed areas are shown below. Note that the abnormal structures are surrounded by a unit membrane associated with ribosomes. Arrowheads indicate ribosomes associated with the ER membrane.