Protists breaking rules

There are a few well-followed rules in biology and it is super fun when they get broken. Researchers in the UK found a single-celled protist in a pond on the Oxford University campus that breaks a rule that every organism from E. coli to alligators follows.

The rule is that there are three kinds of stop signs on mRNA strands. They are UAG, UAA, and UGA. 

Essentially when a cell needs a new protein for a job, it tells other proteins to go in and copy that gene from the DNA. That copy of the DNA is mRNA. Then that mRNA is read and turned into the protein that the cell wanted in the first place. 

But there’s a special genetic language cells use in going from mRNA to protein. The language has four letters and 64 words. Each word is made up of three letters, and they each correspond to a specific amino acid. Those amino acids hook up to build proteins. Many words actually mean the same thing like AAA and AAG both mean “lysine”. 

And in almost every organism, the words UAG, UAA, and UGA mean “stop”. It is super important to stop at the right time otherwise you get proteins that are too long and messed up. 

But the protist these researchers found breaks that stop rule because they changed their language. Instead of UAG, UAA, and UGA all meaning stop, UAG means glutamine, UAA means lysine, and only UGA still means stop. 

We still don’t really understand why they would bother breaking this rule other than random chance, but it is so cool that a single-celled organism found in a university pond broke something this fundamental.

Reference: “Identification of a non-canonical ciliate nuclear genetic code where UAA and UAG code for different amino acids” McGowan et al. PLOS Genetics, 2023.

Add a Comment

Your email address will not be published. Required fields are marked *