Genetic map of the Chlamydomonas reinhardtii mitochondrial genome, including all currently identified optional introns. Protein-coding regions and regions encoding structural RNAs are red and orange, respectively. S1–S4 represent the small-subunit rRNA-coding modules; L1–L8 represent the large-subunit rRNA-coding modules. The terminal inverted repeats (IR) are black. Intronic regions and their open reading frames are boxed in blue inside their associated genes. The C. reinhardtii strains (Table 1) in which the different introns occur are labelled in parentheses. Solid arrows denote the transcriptional polarities. Note: due to the presence/absence of introns among the different strains, the size of the C. reinhardtii mitochondrial genome can vary from 15,782 nt to 18,990 nt.