TABLE 1.

Relative activities of translation initiation factors

Initiation factor	Globin mRNA bindinga		RNA-dependent ATPaseb		Helicase activityc
	−ATP	+ATP	Kact	Vmax	ΔG = −17.9	ΔG = −24.7
eIF4A	130	1800	15,000	110	3.0	0.6
eIF4B	230	350	–d	–d	–d	–d
eIF4F	3610	3990	30	20	7.3	1.3
eIF4A, eIF4B	150	5170	60	135	10.3	3.6
eIF4F, eIF4B	3820	4260	30	30	9.6	3.6

^a Radioactively labeled globin mRNA retention on nitrocellulose filters (cpm) (12).

^b Hydrolysis of [γ-³²P]ATP in response to added RNA (K_act in μm, V_max in fmol of PO₄ released per s per μg of either eIF4A or eIF4F) (13).

^c Unwinding of duplex RNA with a 33-nucleotide single-stranded region or 29-nucleotide single-stranded region; duplexes were 11 and 15 bp, respectively (initial rate of unwinding) (14).

^d — = not determined.