The role of RNA structure in translational regulation by L7Ae protein in archaea

Folding of the A. fulgidus l7ae 5′-UTR k-turn in response to Mg²⁺ ions and L7Ae studied by FRET. The RNA shown at the top was synthesized with 5′ fluorescein donor and Cy-3 acceptor. The nucleotides written in italic extend the A. fulgidus sequence to make a duplex suitable for the FRET experiments. A solution of 20 nM fluorophore-labeled RNA was titrated with either Mg²⁺ ions (lower concentration scale) or L7Ae protein (upper concentration scale) and E_FRET measured in the steady state. E_FRET is plotted as a function of Mg²⁺ ions (open circles) and L7Ae protein (closed circles). The RNA clearly fails to fold in response to the addition of the metal ions. However, addition of L7Ae results in a structural transition, and the data have been fitted (line) to Equation 1.