Table 5.

Effect from Introduction of a G•U Pair in Model Duplexes

	Internal			Terminal
	GU	AU	GC	GU	AU	GC
ΔG (kcal/mol)	−14.6	−15.3	−15.8	−9.6	−9.2	−10.2
Δ ΔG (kcal/mol)	(0)	−0.7	−1.2	(0)	+0.4	−0.6

Duplex stabilities ΔG were measured in thermal denaturation experiments in 1 M NaCl, 10 mM EDTA and 50 mM sodium phosphate, pH 7.0. The sequence of the duplexes was as follows (in the 5′ to 3′ direction, with the base pair being varied underlined): GCCUCUAAAC/GUUUGGAGGC, GCCUCUAAAC/GUUUAGAGGC and GCCUCCAAAC/GUUUGGAGGC for duplexes containing internal GU, AU and GC pairs and GCCUCU/GGAGGC, GCCUCU/AGAGGC and GCCUCC/GGAGGC for duplexes with terminal GU, AU and GC pairs. Δ ΔG values represent stabilities for AU and GC pairs relative to GU pairs. Δ Δ ΔG values represent the additional destabilization of internal GU pairs relative to terminal GU pairs and are calculated by subtracting the Δ ΔG values for terminal GU pairs from the Δ ΔG values for internal GU pairs.