Figure 4.

Catalytic strategies of the small nucleolytic ribozymes. To accelerate self-cleavage, the ribozyme motifs employ, to varying degrees, in-line arrangement (α), neutralization of the non-bridging pro-R_P (O_R) and pro-S_P (O_S) oxygen atoms (β), deprotonation of the attacking 2′ OH (γ) and neutralization of the negative charge at the 5′ oxygen atom (δ) (52,53). Additionally, the 2′ OH can be acidified by hydrogen bond donation to it (γ') or by preventing inhibitory interactions (γ''). Frequently, the N1 atom of a guanine contributes to the γ strategy, and the exocyclic amine of (sometimes the same) guanine to the γ' principle, while the functional groups involved in the realization of the β, γ'' and δ principles are more variable. For details see (54).