Table 2. Sequence variations in the core recognition region of RNA ligands and hierarchy of RNA affinities for T4 and RB69 regA proteins.

T4 regA protein	#1 #11	Kapp (107 M–1)
RB G45	AAGGAAAUAAA	19.9
T4 G44	GAGGAAAUUAU	4.9
T4 G45	AAGGAAAUUAC	3.2
RB G44	GAGGAAAAUUA	2.5
RB regA	AUGGUAAAAAU	1.3
T4 regA	AUGGUAAAAUG	0.8
RB69 regA protein	#1 #11	Kapp (107 M–1)
T4 G44	GAGGAAAUUAU	34.0
RB G44	GAGGAAAAUUA	9.5
T4 G45	AAGGAAAUUAC	2.0
RB G45	AAGGAAAUAAA	1.8
RB regA	AUGGUAAAAAU	0.6
T4 regA	AUGGUAAAAUG	0.16

Nucleotides in bold indicate base substitutions relative to preferred, high affinity RNA.

Underlining indicates RNase protected nucleotides