Mapping of genome-wide action sites of topoisomerase IIbeta by a functional ChIP-chip technique (eTIP-tiling array)

DNA topoisomerase II (topo II) catalyzes a strand passage reaction in that one duplex is passed through a transient brake in another. Completion of late stages of neuronal development depends on the presence of active isoform (topo IIbeta). We identified topo IIbeta action sites on 7 selected genomic regions (about 79 Mb in total), each containing at least one gene that is controlled by topo IIbeta in neuronal differentiation. We used a novel method, etoposide-mediated topoisomerase immunoprecipitation (eTIP), followed by identification of precipitated DNA fragments on genomic tiling arrays. These DNA fragments were first fractionated by concentrated salt prior to the array analysis. The 0.5 M NaCl-released fraction was analyzed as P2 and the salt-resistant fraction wad analyzed as P1. The genomic DNA fractions from the immunoprecipitate (P1 or P2) were co-hybridized with a reference DNA isolated from the input of immunoprecipitation.