Building the machinery of life

A novel Bacillus subtilis riboswitch as described by the authors is an efficient and highly sophisticated on or off control mechanism, with a key regulatory role of switching between burning glycine for energy and using it for protein synthesis. The riboswitch is the first example of a riboswitch that involves complex binding interactions comparable to multiple protein interactions, according to Ronald R. Breaker's group at Yale University, and is the only one so far discovered that switches on gene expression if activated instead of responding in a simple negative-feedback fashion to levels of their target compound. The riboswitch has two domains that bind to glycine, while all other riboswitches only have one binding domain, Breaker said. "Binding of one ligand at one binding site improves the binding affinity of the second ligand to the second binding site," he told The Scientist. "This allows the riboswitch to sense much smaller changes in ligand concentration." Most riboswitches will significantly change the expression of the genes over about a 100-fold change in concentration of ligand, but this one requires only about a tenfold change in concentration of the ligand, making it very sensitive, Breaker said.

In addition to being an interesting discovery that deals with the workings of cells, this illustrates possible steps in the development of the machinery of life the first time, billions of years ago.

Changing the structure of a strand of RNA so it binds to an amino acid at two locations instead of just one increases the sensitivity tenfold. Other things probably had to take place for that change to occur, but those can be teased out with more work. It's easy to imagine a pathway from strands of RNA that served as templates for copying themselves, to strands of RNA that wrapped themselves around amino acids for stability, to strands that wrapped around multiple amino acids, to strands that accidentally built protein chains while they were wrapped around amino acids, to...

There's no guarantee this was the path life originally followed, but the more plausible sequences leading to the origin of life that turn up, the harder it is to argue that we have to go outside the laws of nature to explain the origin of life.