Table 1.

Sequences, melting temperatures and thermodynamic parameters for G-quadruplex folding of the studied oligonucleotides

Sequence name (species)		Sequence (from 5′ to 3′)	NaCl				KCl
			Tm (°C)	ΔH° (kcal mol−1)	ΔS° (cal K−1 mol−1)	ΔG°(310 K) (kcal mol−1)	Tm (°C)	ΔH° (kcal mol−1)	ΔS° (cal K−1 mol−1)	ΔG°(310 K) (kcal mol−1)
G2 motifs
Bom17	(Bombyx)	(GGTTA)3GG	a				a
Asc20	(Ascaris)	(GGCTTA)3GG	a				a
Spom20	(S. pombe)	(GGTTAC)3GG	no G4b				ndc
Spom23	(S. pombe)	(GGTTACA)3GG	no G4b				no G4b
Cgi26	(C. guillermondii)	(GGTGTACT)3GG	no G4				no G4
G3 motifs
Gia18	(Giardia)	(GGGTA)3GGG	60	−53 ± 7	−157 ± 19	−3.7 ± 0.6	68	−63 ± 4f	−185 ± 12f	−5.7 ± 0.4f
Hum21	(H. sapiens)	(GGGTTA)3GGG	59	−55 ± 4	−167 ± 12	−3.7 ± 0.4	65	−60 ± 3	−177 ± 9	−5.0 ± 0.3
Par21	(Parameciumd)	(GGGTTT)3GGG	50	−53 ± 8	−162 ± 23	−2.2 ± 0.5	64	−64 ± 10f	−189 ± 29f	−5.2 ± 0.9f
Scer21	(S. cerevisiae)	(GGGTGT)3GGG	50	−48 ± 5	−148 ± 15	−1.9 ± 0.2	68	−68 ± 8f	−200 ± 25f	−6.2 ± 0.9f
Ara24	(Arabidopsis)	(GGGTTTA)3GGG	57	−60 ± 5	−179 ± 14	−3.6 ± 0.4	64	−73 ± 10	−216 ± 28	−5.7 ± 0.9
	Plasmodiume	(GGGTTYA)3GGG, Y=T or C	55 ± 2	−53 ± 4	−158 ± 11	−2.8 ± 0.4	64 ± 1	−63 ± 5	−186 ± 14	−4.9 ± 0.6
Tom24	(L. esculentumd)	(GGGTTAA)3GGG	51	−54 ± 4	−168 ± 13	−2.3 ± 0.2	64	−77 ± 5	−228 ± 13	−6.1 ± 0.4
Chla27	(Chlamydomonas)	(GGGTTTTA)3GGG	46	−56 ± 4	−176 ± 13	−1.6 ± 0.3	57.5	−68 ± 8	−207 ± 24	−4.2 ± 0.6
G4 motifs
Tet22	(Tetrahymena)	(GGGGTT)3GGGG	64	−54 ± 8	−161 ± 24	−4.4 ± 0.7	>80
Oxy28	(Oxytricha)	(GGGGTTTT)3GGGG	66	−82 ± 13	−242 ± 38	−6.9 ± 1.3	>80
G3/G4 motif
Gla26	(C. glabrata)	G4T(CTG3TGCTGTG4T)CTG3	48	−53 ± 12	−164 ± 36	−1.8 ± 0.5	63	−70 ± 12	−206 ± 34	−5.4 ± 0.8

The number in the sequence name denotes the sequence length (in nucleotides); telomeric motifs are in italic font.

Melting temperatures (T_m) reported in this table depended neither on wavelength nor on oligonucleotide strand concentration (3, 10 and 30 µM).

Melting curves at 295 nm were analysed according a two-state equilibrium model and assuming linear low- and high-temperature absorbance baselines. Standard enthalpy and entropy changes (ΔH° and ΔS°) for folding were determined by linear fitting lnK versus 1/T, where K is the equilibrium constant between the folded and the unfolded state; standard Gibbs free energy changes (ΔG°) were extrapolated at 310 K, from the relation ΔG°(T) = ΔS° – TΔS°. ΔH°, ΔS° and ΔG° reported in this table are the mean values obtained from analysis of melting curves at 3 and 30 µM strand concentration upon varying linear low- and high-temperature absorbance baselines ± maximum deviation.

^aThe presence of a G-quadruplex and of a non-G-quadruplex competing structure made T_m determination not straightforward.

^bA very minor fraction of oligonucleotide may be folded into G-quadruplexes at low temperatures.

^cNot determined: T_m of Spom20 in KCl could not be determined accurately because of the incertitude in low-temperature absorbance baseline.

^dParamecium and L. esculentum (tomato plant) have degenerated telomeric motifs: GGGKTT in Paramecium (K=T or G) and GGGTTWA (W=A or T) in tomato plant; for W=T, the tomato telomeric motif comes back to the Arabidopsis one; for K=G, the Paramecium telomeric motif comes back to the Tetrahymena one.

^eData from a previous study (65) (mean values from analysis of the eight possible variant sequences); for Y=T, the Plasmodium telomeric sequence comes back to the Arabidopsis one.

^fFor Gia18, Par21 and Scer21 in KCl at 30 µM strand concentration a two-state model is not appropriate, as revealed by non-denaturing PAGE; nevertheless linear van’t Hoff graphs were obtained.