A Little More Land

A recent ScienceDaily article summarized a July 18 paper in the journal Science that described the mechanism by which a type of RNA is able to regulate gene expression in some bacteria. It was already known that this RNA, cyclic di-guanosine monophosphate (di-GMP), was a so-called second messenger molecule in bacteria. Basically, di-GMP is generated and diffused in a bacterium, signalling the activation of various proteins which lead to a wide range of changes in activity such as motility, changes in virulence, and biofilm formation. What wasn’t known was just how di-GMP was able to regulate gene expression. The authors of the paper found that this was accomplished via an interesting and relatively recently discovered set of molcules called riboswitches.

The lab of the lead author, Ronald Breaker, discovered riboswitches just a few years ago. They are essentially a small part of an mRNA molecule that has the ability to bind to various metabolites. The part of the riboswitch that is able to bind is known as the apatamer. The apatamer binding is very selective, only applying to particular molecules for the various riboswitch types. More and more types are being discovered, but most of the current ones are listed here. Once the apatamer has undergone binding, the other part of the riboswitch, the expression platform, is changed in response. This expression platform is what then affects gene expression. (I am not very clear on how that step works, nor have I been able to find much information on it as of yet).

This discovery is especially interesting because basically all such fundamental genetic activations in cells were thought to be brought about by proteins, not RNA. It helps illuminate our understanding of some of the earliest ancient lifeforms on Earth, for in providing an alternative for proteins it provides and escape from the circular issue of how either DNA or proteins evolved without the other being present. RNA may very well have filled some of the critical roles before proteins came on the scene. This idea is central to the validity of the RNA World hypothesis.

Tags: Genetics, Molecular Biology