Table 1.

Mss116p has RNA-dependent ATPase activity

Nucleic acid	kcat (min−1)
Tt LSU- P5abc	72 ± 8
Sc aI5γ	112 ± 6
Sc bI1	110 ± 14
Poly(A)	90 ± 26
Poly(C)	62 ± 12
Poly(G)	n.d.
Poly(U)	54 ± 16
Poly(dA)	n.d.
Poly(dC)	10 ± 2
-RNA	n.d.

ATPase activity was assayed in reaction medium containing 100 mM KCl/8 mM MgCl₂ at 30°C with 50 nM Mss116p in the presence of saturating unlabeled ATP (3 mM) and RNA (300 nM for intron RNAs and 0.25 μg/μl for oligonucleotides). The table summarizes k_cat values determined by measuring the initial rate (r₀), corresponding to <1% of final product in a 100-min time course at saturating ATP and RNA concentrations; all reactions were linear for >15 min. Saturation was confirmed by measuring r₀ at multiple RNA concentrations. K_m^ATP values for a subset of RNAs were determined by measuring r₀ at a series of saturating and subsaturating ATP concentrations: Tt LSU-ΔP5abc, K_m^ATP = 88 ± 30 μM; Sc aI5γ, K_m^ATP = 171 ± 25 μM; Sc bI1, K_m^ATP = 222 ± 40 μM; poly(C), K_m^ATP = 633 ± 98 μM. Based on these results, 3 mM ATP was assumed to be saturating for all RNAs. All values are the mean ± the standard deviation for triplicate assays. n.d., not detectable above background.