Table 1. Kinetic parameters (k_unw^max and K_1/2) of Mtr4 mutants for unwinding poly(A) and non(A) substrates^a.

	poly(A)	non(A)	poly(A)	non(A)
Enzyme	kunwmax (min−1)	kunwmax (min−1)	K (nM)	K (nM)
Mtr4WT	0.59 ± 0.05	0.34 ± 0.05	252 ± 60	255 ± 116
Mtr4archless	0.49 ± 0.07	0.34 ± 0.08	221 ± 93	260 ± 164
Mtr4R1030A	0.18 ± 0.02	0.16 ± 0.03	51 ± 26	129 ± 92
Mtr4E1033A	1.08 ± 0.09b	1.17 ± 0.24b	504 ± 93	1415 ± 468
Mtr4E1033W	0.22 ± 0.07	undetermined	484 ± 360	undetermined
Mtr4R1030A/E1033A	0.52 ± 0.1	0.41 ± 0.04	498 ± 216	269 ± 81
Mtr4R1030A-archless	n.d.	n.d.	n.d.	n.d.
Mtr4E1033A-archless	n.d.	n.d.	n.d.	n.d.

Data presented here represent averages from three independent experiments; error bars represent SD. n.d., no unwinding activity detected.

^aMethodologies and equations used to derive kinetic constants are found in the ‘Materials and Methods’ section.

^bSince the curve for the Mtr4^E1033A catalyzed unwinding never reached saturation, calculated k_unw^max rates between poly(A) and non(A) appear within error, although a clear distinction between RNA substrates is observed at every tested concentration (see Figure 3).