FIGURE 8.

The N-terminal and linker domains modulate locking of the yTop1-clamp⁴⁶⁰. A, exponential cultures of top1Δ cells transformed with the indicated YCpGAL1-yeast and human top1 chimeras were serially diluted and spotted onto SC-uracil plates supplemented with dextrose (Dex) or galactose (Gal), 25 mm HEPES (pH 7.2), 0.125% Me₂SO, and the indicated concentrations of CPT. Cell viability was assessed after incubation at 30 °C. B, crude cell extracts of galactose-induced cultures were corrected for protein concentration, serially 10-fold diluted, and incubated in plasmid DNA relaxation assays as described under “Experimental Procedures.” Lane C, plasmid DNA control. (R) and (-), the positions of relaxed and supercoiled DNA, respectively.