Fig. 2.

Measuring the fraction of mant nucleotides bound specifically to the fiber. The fiber was first incubated in mantATP and at 100 s chased with ATP similar to the control fiber in Fig. 1, red squares. The fit to the decay curve during the chase defined P2 = 0.29 ± 0.01; T2 = 170 ± 7 s. The fiber was then washed with rigor buffer and incubated again, in mantATP with an additional 4 mM ATP. The presence of the ATP competes off mantATP from sites that bind ATP specifically, blue circles. As can be seen, approximately half of the nucleotides are no longer bound to the fiber. An average of ten experiments showed 42 ± 3% of the nucleotides bound nonspecifically. The fiber was then chased with ATP starting at 100 s. The slow release of nucleotides seen in the absence of competing ATP is much reduced, showing that the slow release of nucleotides comes from ATP specific sites. A fit to the data during the chase defined P2 = 0.05 ± 0.02, T2 = 160 ± 15 s. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)