Date of Award


Document Type

Honors Thesis

Degree Name

Bachelor of Science



First Advisor

Carla Theimer


Riboswitches are a type of RNA structure found on messenger RNAs that function in gene expression regulation. The preQ1 riboswitch is particularly interesting to study because it contains a relatively small aptamer binding region and it is not essential in E. coli for the organism's survival, allowing in vivo experimentation in a viable organism. Upon ligand binding to the aptamer, a hairpin-type RNA pseudoknot forms, which functions to turn off the gene using a premature transcriptional termination mechanism. However, in some species studied, this terminator hairpin possesses enough thermodynamic stability that it is doesn't unfold upon release of the ligand. Based on this, it has been shown that the terminator and anti-terminator hairpins are capable of coexisting in the absence of the ligand. Thermodynamics play a large role in determining the actual degree of the translational control. It was found in previous experiments that the greater the stability of the terminator hairpin, the less reporter gene (firefly luciferase) activity recorded. When the aptamer-anti-terminator hairpin conformation is present, luciferase activity was found to be roughly double. Since it is possible for both hairpins to be present, the gene is not either turned off or on completely. This allows for the ability for partial effects (differential degrees of control). These different expression patterns have been explored for different species that contain this riboswitch.

Included in

Biology Commons