de Vasconcelos Júnior, Antônio AlexandreTirado-Velez, JMMartin-Galiano, Antonio JavierMegías, DiegoFerrandiz-Avellano, Maria-JoseHernández, PabloAmblar, Monicade la Campa, Adela G2023-05-182023-05-182023-03-22Int J Mol Sci. 2023 Mar 22;24(6):5973.http://hdl.handle.net/20.500.12105/16096The DNA topoisomerases gyrase and topoisomerase I as well as the nucleoid-associated protein HU maintain supercoiling levels in Streptococcus pneumoniae, a main human pathogen. Here, we characterized, for the first time, a topoisomerase I regulator protein (StaR). In the presence of sub-inhibitory novobiocin concentrations, which inhibit gyrase activity, higher doubling times were observed in a strain lacking staR, and in two strains in which StaR was over-expressed either under the control of the ZnSO4-inducible PZn promoter (strain ΔstaRPZnstaR) or of the maltose-inducible PMal promoter (strain ΔstaRpLS1ROMstaR). These results suggest that StaR has a direct role in novobiocin susceptibility and that the StaR level needs to be maintained within a narrow range. Treatment of ΔstaRPZnstaR with inhibitory novobiocin concentrations resulted in a change of the negative DNA supercoiling density (σ) in vivo, which was higher in the absence of StaR (σ = -0.049) than when StaR was overproduced (σ = -0.045). We have located this protein in the nucleoid by using super-resolution confocal microscopy. Through in vitro activity assays, we demonstrated that StaR stimulates TopoI relaxation activity, while it has no effect on gyrase activity. Interaction between TopoI and StaR was detected both in vitro and in vivo by co-immunoprecipitation. No alteration of the transcriptome was associated with StaR amount variation. The results suggest that StaR is a new streptococcal nucleoid-associated protein that activates topoisomerase I activity by direct protein-protein interaction.engVoRDNA gyraseDNA supercoilingDNA topoisomerase IStaRNucleoid-associated proteinsSupercoiling homeostasisSupercoiling regulationTopsoisomerase regulatorDNA Topoisomerases, Type IStreptococcus pneumoniaeHumansNovobiocinDNA, BacterialDNA GyraseStaR Is a Positive Regulator of Topoisomerase I Activity Involved in Supercoiling Maintenance in Streptococcus pneumoniaeAtribución 4.0 Internacional36983048246597310.3390/ijms240659731422-0067International journal of molecular sciencesopen access