It's the 3' (3-prime) UTR (un-translated region). It can affect the translation of the mRNA. https://en.wikipedia.org/wiki/Three_prime_untranslated_region#:~:

It's the 3' (3-prime) UTR (un-translated region). It can affect the translation of the mRNA. https://en.wikipedia.org/wiki/Three_prime_untranslated_region#:~:text=In%20molecular%20genetics%2C%20the%20three,post%2Dtranscriptionally%20influence%20gene%20expression https://en.wikipedia.org/wiki/Three_prime_untranslated_regio.... The next thing is the poly-A tail: https://en.wikipedia.org/wiki/Polyadenylation https://en.wikipedia.org/wiki/Polyadenylation blasting the 3' UTR, we see it ~50% of it was copied from the human mitochondria tldr, extra regulatory signals (often not well understood)