Figure 1.

Mss116p duplex-unwinding and strand-annealing activities. Reactions were done with RNA oligonucleotides that form a 16-bp duplex with (a) a 25-nt 5′ overhang; (b) a 25-nt 3′ overhang; or (c) blunt-ends. For each substrate, the figure shows representative duplex- unwinding reactions with 2 mM ATP (left panels), strand-annealing reactions without ATP (middle panels), and strand-annealing reactions with 2 mM ATP (right panels). Plots beneath the gels show fraction duplex versus reaction time fitted to the integrated form of a homogenous first-order rate law. Substrates and products are depicted schematically to the left of the gel, with the asterisk indicating the radiolabel and the vertical arrow indicating the direction of the reaction. Gray arrows indicate presence and white arrows indicate absence of ATP in the reactions. The zero time points for the duplex-unwinding reactions were recorded before ATP addition, and the zero time points for the strand-annealing reactions were recorded before Mss116p addition. Strand annealing in the absence of Mss116p was not significant (<5% of the RNA spontaneously annealed within 10 min; data not shown). Rate constants calculated from at least two independent time courses for each reaction are summarized in Table 3.