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DNA topoisomerase IB, C-terminal catalytic domain. Topoisomerase I promotes the relaxation of both positive and negative DNA superhelical tension by introducing a transient single-stranded break in duplex DNA. This function is vital for the processes of replication, transcription, and recombination. Unlike Topo IA enzymes, Topo IB enzymes do not require a single-stranded region of DNA or metal ions for their function. The type IB family of DNA topoisomerases includes eukaryotic nuclear topoisomerase I, topoisomerases of poxviruses, and bacterial versions of Topo IB. They belong to the superfamily of DNA breaking-rejoining enzymes, which share the same fold in their C-terminal catalytic domain and the overall reaction mechanism with tyrosine recombinases. The C-terminal catalytic domain in topoisomerases is linked to a divergent N-terminal domain that shows no sequence or structure similarity to the N-terminal domains of tyrosine recombinases.
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Jiyao W et al.(2023). "The conserved domain database in 2023.",