Fig. 1

C. elegans has high levels of mitochondrial rRNA despite their mtDNA organization: a Schematic of human mitochondrial DNA (mtDNA). Human mtDNA encodes 13 essential components of the electron transport chain (depicted in green), 22 tRNAs (gray) and 2 rRNAs (magenta) required for mitochondrial translation. Human mtDNA contains three promoters: heavy strand promoter 1 (HSP1) drives expression of the rRNAs independently from the rest of the genome; heavy strand promoter 2 (HSP2) drives expression of the entire mtDNA heavy strand as a polycistronic transcript; light strand promoter (LSP) drives the transcription of the entire mtDNA light strand. b Schematic of C. elegans mtDNA. All of the genes in C. elegans mtDNA are presumed to be transcribed from a single heavy strand promoter (HSP) as a single polycistronic transcript. c Metazoan phylogeny. Asterisks indicate taxa containing species with mtDNA organization similar to C. elegans (rRNA encoding genes are distant from each other and mtDNA transcription occurs from a single apparent promoter). Tree branch length is arbitrary. d Relative RNA levels of C. elegans mitochondrial genes normalized to ND4 levels (n = 4 for each of the genes. COI: \( \bar{x} \) = 2.07, SD = 0.15; COII: \( \bar{x} \) = 0.86, SD = 0.09; COIII: \( \bar{x} \) = 1.35, SD = 0.24; ND1: \( \bar{x} \) = 0.27, SD = 0.03; ND4: \( \bar{x} \) = 1.00, SD = 0.11; ND5: \( \bar{x} \) = 0.80, SD = 0.16; 12S: \( \bar{x} \) = 45.61, SD = 8.71; 16S: \( \bar{x} \) = 201.7, SD = 52.24)