From the phenomenon of frameshift, we see that the same nucleotide sequence
could encode different amino acid sequences. This allows two genes with entirely different
protein products to share the same nucleotide sequence. The gene overlapping is
often found in a compact genome such as HBV and HIV.
In human mitochondrial DNA, there are two
overlapping genes: ATPase subunits 6 and 8.
Figure 5-C-3. An example of gene overlapping.
The gene of ATPase subunit 8 is located between 8366 and 8569 of the human
mitochondrial genome. The gene of ATPase subunit 6 is located between 8527 and
9204. ATPase 8 contains 68 amino acids while ATPase 6 has 226 amino acids.
Their amino acid sequences are different even in the region where they share the same DNA
sequence. It is interesting to note that the end of
the ATPase 6 gene is not a stop codon, but two nucleotides "TA". It
becomes the stop codon "TAA" only after the poly-A tail is added during RNA