Table 1. Comparison of binding affinities (K_D's).

Sigma	Method	Max [Core] (nM)	Salt	[Salt] (mM)	KD (nM)
σ70
	FRET1	?	KCl	250	≥1
	HPLC gel filtration1	>1000	KCl	250	≥10
	FRET2	40	KCl	200	0.3
	SPR3	490	NaCl	150	190
	SEC4	400	NaCl	200	0.3
	LRET	10	NaCl	100	8
			NaCl	250	50
			NaCl	500	300
			Kglu	100	3
			Kglu	250	17
			Kglu	500	21
σ32
	SEC4	400	NaCl	200	1.24
	in vitro transcription 5	100	NaCl	100	1
	LRET	10	NaCl	100	0.8
			NaCl	250	0.6
			NaCl	500	2.4
			Kglu	100	0.3
			Kglu	250	1.3
			Kglu	500	2

¹Binding studies performed by Gill et al. (1991).

²Binding studies performed by Wu et al. (1976).

³Surface plasmon resonance studies performed by Ferguson et al. (2000).

⁴Size exclusion chromatography studies performed by Maeda et al. (2000).

⁵ In vitro transcription studies performed by Joo et al. (1997).