Figure 4.

Summary of effects on equilibrium constants from IGS extension (dark columns) and the formation of the P1 extension (light columns) on the ribozyme reaction. Equilibrium constants are defined in Figure 2A. $K_d^{\mathit{UCGA}\prime }$ refers to binding of UCGA (dark columns) or UCGAAACC (light columns) in the presence of bound P. Similarly, $K_d^{S^{\prime }}$ refers to binding of –1d,rSA (dark columns) or –1d,rSA₃C₂ (light bars) in the presence of bound UCG. All values are relative to the L-21 ScaI reaction and were calculated from Figure 2. Effects from the IGS extension were determined from comparison of reactions with the L-16 ScaI ribozyme that has CCUCdTA bound. The combined effects from the IGS extension and formation of base pairs with that extension were determined from reactions of the L-16 ScaI ribozyme with CCUCdTAAACC bound.