FIGURE 1.

Reaction pathway for Pol I(KF) from DNA binding up to phosphoryl transfer. DNA* (step 2.1) represents a DNA rearrangement detected with a 2-AP probe 5′ to the templating position. E_O and E_C (step 2.2) represent the open and closed conformations of the polymerase. E_C to E_C^‡ (step 3) represents a further transformation, whose identity is not known, corresponding to the rate-limiting step in single nucleotide incorporation. The existence of additional, as yet undetected, steps is not ruled out.