Figure 1.

Secondary structure of an active ribozyme. A single point mutation (G⁵ to A, or A¹⁴ to G; circled) eliminates the ribozyme activity (20, 46). It is to be noted that the catalytic loop containing G⁵ and A¹⁴ captures Mg²⁺ ions, since a hammerhead ribozyme is a metalloenzyme (48–57).