Ultra Conserved Elements: Poison Exons in DNA
Why in the news
A new study offered an explanation for why ultra conserved elements (UCEs) have stayed unaltered for so long.
About UCEs
- Long identical DNA stretches (over 200 bp) shared by humans, rats and mice from a common mammal ancestor, and conserved in chickens, dogs and fish too.
- Most do not code for proteins, so their role was long unknown.
The discovery
- David J. Elliott (Newcastle): a UCE in the mouse Tra2b gene is a poison exon tied to RNA splicing.
- Located in the gene’s first intron; when abundant Tra2 protein triggers its inclusion in mRNA, premature stop codons halt production and the mRNA is lost.
- This works as a self-limiting brake on Tra2 protein.
Sperm and infertility
- Removing the UCE in mouse sperm-producing cells led to excess Tra2 protein, cell death and infertility.
- Mutations are thus wiped out before being passed on, keeping UCEs unchanged.
Wider meaning
- Not every UCE acts this way.
- Shows that vital regulatory roles can sit in non-coding ‘junk DNA’.
Exam angle
- Terms: UCE, poison exon, intron, RNA splicing, stop codon.