If you’re reading this, you’re probably a eukaryote. This is the name given to complex life forms with cells that contain nuclei and other specialized organelles. However, while most of us take these characteristics for granted, scientists have spent several decades trying to identify the particular genetic event that enabled such wonderfully intricate beings to evolve from basic bacterial sludge – and they may have finally cracked it.
The development of eukaryotic cells would not be possible without certain enzymes called kinases, which catalyze the addition of phosphate groups to proteins in order to activate them for a wide range of functions. Without this, many of the complex processes that occur within our cells would simply not be able to take place.
Some kinases also catalyze the synthesis of phosphatidylcholine, which is a key component of eukaryotic membranes that enclose and compartmentalize the various components of eukaryotic cells. Prokaryotes, meanwhile, are single-celled organisms that lack kinases, and therefore contain no such membranes.
The development of the earliest gene coding for the synthesis of kinases therefore marks a significant milestone in life’s evolution, as it enabled eukaryotes to emerge from prokaryotes. As such, every complex organism on the planet owes its existence to this single ancestral gene, although because so many different types of kinases now exist, identifying this gene has proven quite a challenge.
However, a new study in the Journal of Biological Chemistry provides evidence that all kinases arose from an ancient version of a gene known as GlnRS, which codes for another enzyme called glutaminyl aminoacyl-tRNA synthetase. This compound facilitates the transcription – or reading – of DNA in order to enable the formation of proteins.
To determine this, the researchers compared the structures of a range of kinases found in six different organisms, including humans, in order to identify common sequences of amino acids – the individual units that make up proteins. They then used a genetic database to search for genes capable of coding for proteins containing these common sequences, and found GlnRS to be the “only candidate.”
As such, this gene – or an ancient version of it – appears to be the common ancestor of all kinases, and therefore of all multicellular organisms on Earth.