Figure 5. Amino acids 489-587 in BLM are necessary for enhancing BLM unwinding by topoisomerase IIα.

(A) Autoradiograph of time-course helicase assays with 2 fmoles of 3’ overhang substrate and indicated amounts of BLM or BLM^Δ489-587 (left panel) or wild-type BLM (right panel) with and without topoisomerase IIα. Quantification of percent unwinding by BLM^Δ489-587 or wild-type BLM with equimolar topoisomerase IIα is shown. Only wild-type BLM is stimulated by topoisomerase IIα. Minus ATP (-ATP) control indicates ATP-dependent unwinding of substrate and (▲) depicts completely unwound heat-denatured substrate. (B) Increasing concentrations of topoisomerase IIα (0 – 10 nM) do not stimulate BLM^Δ489-587 but stimulate wild-type BLM. Helicase assays were carried out with different concentrations of topoisomerase IIα and a fixed concentration of BLM (1 nM) for 10 mins.