Table 1. Summary of structural features and binding thermodynamics.

	hnRNP A1 RRM1	SRSF1 pseudo-RRM2	hnRNP F qRRM1	Tra2β1 RRM	ΔNTra2β1
5΄ RNA 3΄ §	UUAGGU	AAGGAC	AGG*G*AU	AAGAAC	AAGAAC
Binding mode	Canonical (β-sheet)	Pseudo-RRM (α-helix 1)	quasi-RRM (Loops)	Canonical + N and C-termini	Canonical + C-terminus
Intermolecular hydrogen bonds	5	5	5	6	5
Hydrophobic interactions	3	2	3	3	3
Mean ΔGobs (kcal mol−1)	−8.0 ± 0.5	−9.9 ± 0.3	−8.7 ± 0.2	−8.8 ± 0.3	−8.4 ± 0.2
ΔGPE/(%)	28	26	10	23	ND
ΔGnPE/(%)	72	74	90	77	ND
ΔCp,obs/cal K−1 mol−1	−130 ± 27	−338 ± 17	−40 ± 30	−300 ± 23	−166 ± 40
ΔCpf,ASA/cal K−1 mol−1	−96	−90	−164	−348	−263
ΔCpb,ASA/cal K−1 mol−1	−84	−10	−29	−131	−115

^§RNA sequence used in study. Nucleotides specifically recognized by the RRMs are highlighted in bold. *7-deazaguanine. ND: not determined. ΔG_obs was determined by ITC in 20 mM CH₃COOH, 50 mM L-arginine, 50 mM L-glutamate, 0.05% β-mercaptoethanol–NaOH pH 5.5 at different temperatures (see also Table 2). The mean ΔG_obs was obtained by averaging ΔG_obs across the considered temperature range. ΔG_PE and ΔG_nPE are the percentage contributions of the polyelectrolyte effect (ion-release) and non-polyelectrolyte effect to the overall free energy of binding at 1M Na⁺ concentration, respectively. To determine ΔG_PE and ΔG_nPE, ITC titrations were performed at 283.15 K temperature in 20 mM CH₃COOH, 50 mM L-arginine, 50 mM L-glutamate, 0.05% β-mercaptoethanol–NaOH pH 5.5 and different concentrations of NaCl salt (see Figure 5A). ΔC_p,obs is the observed experimental heat capacity. ΔC_p^b_,ASA and ΔC_p^f_,ASA are the expected heat capacities semi-empirically calculated using the bound or free conformations of the binding components, respectively.