Identification of sams-1 mutants and TEM analysis of lysosomes in cbs-1 animals expressing SCAV-3::APEX. (A) Schematic representation of the sams-1 gene (top) and comparison of C. elegans SAMS-1 with human MAT1A and MAT2A proteins (bottom). In the gene diagram, filled boxes represent exons, and thin angled lines represent introns. The EMS-induced mutations (yq547 and yq548) and the deletion allele (tm3945) are indicated. In the protein diagrams, the mutation sites in SAMS-1 are marked with arrowheads. Blue boxes indicate the SAM synthetase N-terminal (SAM_synt_N), middle (SAM_synt_M), and C-terminal (SAM_synt_C) domains. Numbers indicate AA positions. Scale bars: 200 bp (gene) and 100 AA (protein). (B)sams-1 mutations suppress lysosomal defects in cbs-1(yq357) mutants. Left: Images of mKate2::GFP::LGG-2-labeled lysosomes in the hypodermis and muscle in cbs-1(yq357) single mutants and double mutants of indicated sams-1 mutations with cbs-1(yq357). Bars, 5 μm. Right: quantification of the ratio (GFP/[GFP+mKate2]) of fluorescence intensities of lysosomes as shown in the left images. ≥20 lysosomes in the indicated tissues from 3 animals of each genotype were analyzed. Data (mean ± SEM) are from three independent experiments. (C) TEM images of lysosomes in the hypodermis in WT and cbs-1(yq357) animals expressing SCAV-3::APEX. Lysosomes without and with the staining by DAB, which indicates the activity of lysosome-localized SCAV-3::APEX, are shown. White and yellow arrowheads indicate lysosomal membranes without or with DAB staining, respectively. For all quantifications, statistical comparisons were performed using one-way ANOVA with Holm–Sidak’s multiple comparisons test. ****P < 0.0001.