The entire human topoisomerase IT alpha (hTopoII alpha) dimer was expressed
in the yeast Saccaromyces cerevisiae, purified to homogeneity, and subject
ed to atomic force microscopy (AFM) under a tapping mode. Molecular images
obtained exhibited a 'heart or donut-like' structure with a large axial hol
e. The main benefit of the application of AFM to study the hTopoII alpha is
that clear images of the internal 'pore' have been achieved without crysta
llization, staining, or fixation of the sample. These images are consistent
with the model in which topoisomerase II has a large internal gate for DNA
strand passage.