Fig. 1: Mitochondrial gene organization in the Tuatara.
Arrangements are depicted as a linear bar for what is a circular molecule. A The standard vertebrate mt-gene order presumptive as ancestral among vertebrates. B The mt-gene order discovered in complete mt-genomes of the Tuatara. C The standard vertebrate mt-gene order as in “A” above. Abbreviations for genes are: 12 S and 16 S for small and large ribosomal RNAs; NDl–6 and 4 L for NADH dehydrogenase subunits; COI–III for cytochrome c oxidase subunits; Cytb for cytochrome b; 6 and 8 for ATPase subunits. All protein-coding genes are transcribed from the heavy strand with the exception of ND6 from the light strand. Transfer RNA genes are represented by their standard one-letter amino acid codes positioned on the strand encoded, with the top representing the heavy strand and the bottom representing the light strand. S1, S2, Ll, and L2 depict tRNASer(AGY), tRNASer(UCN), tRNALeu(UUR), and tRNALeu(CUN), respectively. The identical and duplicated tRNALeu(CUN) is labeled L2. The Control Region (OH), responsible for heavy-strand replication, standardly has one copy among vertebrates. Identified are three non-coding regions labeled NC1–3 and putative Control Regions. Black bars indicate protein-coding regions rearranged relative to the standard vertebrate mt-genic organization. Eight novel features of the Tuatara mt-genome are numbered with arrows. (1) The origin of light-strand replication (OL) is not present in the Tuatara19 but a stem-and-loop structure overlapping tRNA genes may supplement (Fig. 4), which is indicated by an arrow. (2) The bold italic K represents a duplicated tRNALys that appears to be a pseudogene8. (3) ND6 and tRNAGlu are moved relative to the standard vertebrate mt-genic organization. (4) tRNALeu(CUN) and ND5 are moved relative to the standard vertebrate mt-genic organization. (5) Cytb is moved relative to the standard vertebrate mt-genic organization. (6) tRNAHis is moved relative to the standard vertebrate mt-genic organization. (7) tRNAThr is moved relative to the standard vertebrate mt-genic organization. (8) tRNASer(AGY) is moved relative to the standard vertebrate mt-genic organization. The two identical or near identical copies of tRNALeu(CUN) flank the missing region of all previously reported Tuatara mt-genomes5,6,7 (horizontal green bar).
