PubMed · 6161292
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L Breeden, M Yarus. 1980. Mutations that overcome plasmid-mediated relaxation affect (p)ppGpp.. https://doi.org/10.1007/bf00268453
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Although all other topoisomerases have a broad phylogenetic distribution, DNA topoisomerase V, the major component of the ThermoFidelase sequencing kit, is presently only known in a single species--the archaeon Methanopyrus kandleri. Resolution of the structure of this enzyme by Taneja and co-workers now reveals that this atypical topoisomerase has no structural similarity with other proteins. So, where did it come from? It is my contention that Topo V, and many other orphan proteins, could have a viral origin.
The papillomavirus (PV) E2 protein plays a role in recruiting viral and cellular DNA replication factors, such as PV E1 or RPA to PV genomes. Using both purified proteins and through co-precipitation, it was determined that HPV-11 E2 binds human topoisomerase I. E2 can stimulate topoisomerase I DNA relaxation activity 3- to 4-fold. Conversely, topoisomerase I is unable to stimulate E2 DNA binding. These findings suggest that stimulation of topoisomerase I by E2 may help promote efficient relaxation of the torsional stress induced by PV DNA replication.
Human topoisomerase I is a nuclear enzyme that catalyses DNA relaxation and phosphorylation of SR proteins. Topoisomerase I participates in several protein-protein interactions. We performed a proteomic analysis of protein partners of topoisomerase I. Two methods were applied to proteins of the nuclear extract of HeLa cells: a co-immunoprecipitation and an affinity chromatography combined with mass spectrometry. Complexes formed by topoisomerase I with its protein partners were immunoprecipitated by scleroderma anti-topoisomerase I antibodies. To identify binding sites for the protein partners, baits corresponding to fragments of topoisomerase I were constructed and used in the affinity chromatography. The N-terminal domain and the cap region of the core domain appeared to be the main regions that bound proteins. We identified 36 nuclear proteins that were associated with topoisomerase I. The proteins were mainly involved in RNA metabolism. We found 29 new and confirmed 7 previously identified protein partners of topoisomerase I. More than 40% proteins that associate with the cap region contain two closely spaced RRM domains. Docking calculations identified the RRM domains as a possible site for the interaction of these proteins with the cap region.