Patterns of Codon Usage Across Unicellular Eukaryotes

The genetic code shows redundancy, with 20 amino acids being encoded by 61
codons. Gene sequencing has shown that codons are not used at equal frequency.
Different species show biases towards different sets of codons and different genes
within the same genome may differ in their silent base composition. Most studies on
codon usage bias have centred on either bacteria or multicellular eukaryotes. It has
been proposed that three forces may interact to drive codon bias. Natural selection
can favour a suite of “optimal codons” that may increase the accuracy or efficiency of
protein translation. Local or global mutation pressure can also influence codon bias
towards either GC or AT-ending codons and genetic drift may result in codon bias in
a random fashion.

Here I present patterns of codon usage in the closest unicellular relatives of Metazoa
and highlight the evolutionary forces that drive codon usage bias in three species.
Despite sharing a common ancestor over one billion years ago the three species
show remarkably similar codon bias, with natural selection driving bias towards a
limited number of codons. The data show that the earliest stem-group metazoans
modified their tRNA molecules for eight amino acids (TAPSILVR), through the
deamination of adenosine to inosine. In the final part of the talk I will discuss the
origin of eukaryotic tRNA deamination, showing the mechanism provides a selective
advantage in a broad range of unicellular eukaryotes.

The seminar will be hosted using Zoom. A Google calendar invite featuring the Zoom link will be sent to Biology staff and students before the seminar date. For all enquiries please contact Biology DMT Hub.