Topoisomer_IB_N_1: A subgroup of the N-terminal DNA binding fragment found in eukaryotic DNA topoisomerase (topo) IB. Topo IB proteins include the monomeric yeast and human topo I and heterodimeric topo I from Leishmania donvanni. Topo I enzymes are divided into: topo type IA (bacterial) and type IB (eukaryotic). Topo I relaxes superhelical tension in duplex DNA by creating a single-strand nick, the broken strand can then rotate around the unbroken strand to remove DNA supercoils and, the nick is religated, liberating topo I. These enzymes regulate the topological changes that accompany DNA replication, transcription and other nuclear processes. Human topo I is the target of a diverse set of anticancer drugs including camptothecins (CPTs). CPTs bind to the topo I-DNA complex and inhibit religation of the single-strand nick, resulting in the accumulation of topo I-DNA adducts. In addition to differences in structure and some biochemical properties, Trypanosomatid parasite topos I differ from human topo I in their sensitivity to CPTs and other classical topo I inhibitors. Trypanosomatid topos I have putative roles in organizing the kinetoplast DNA network unique to these parasites. This family may represent more than one structural domain.
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