Inferred intermediate steps from the ancestral gene order to that of the C. azureus mitogenome. Protein-coding genes and CRs are indicated by boxes, and the tRNA genes are indicated by columns. Genes labeled above the diagram are encoded by the H-strand, those below the diagram by the L-strand. The LSP and HSP indicate the light-strand and heavy-strand promoters, respectively; CSB indicates Conserved Sequence Block. The direction of transcription is shown by arrows. The copied tRNA-N are marked by triangles. (A) ancestral gene order; (B) The dimeric molecule with two monomers linked head-to-tail; The locations of LSP1, 2, HSP1, 2 and tRNA-L(UUR)
, 5’ end of CR indicate the proposed positions for transcription initiation and termination of the two monomers. (C) Functional loss of LSP2, HSP2; broken line indicates the disabled transcription regions; Dark gray box indicates the degeneration of LSP2, HSP2 and related genes. (D) Proposed translocation of tRNA-D is shown by arrow. (E) Gene order of the C. azureus mitogenome.