PSF/p54(nrb) stimulates "jumping" of DNA topoisomerase I between separate DNA helices.
We have previously shown [Straub et al. (1998) J. Biol. Chem. 273, 26261] that the pyrimidine tract binding protein associated splicing factor PSF/p54(nrb) binds and stimulates DNA topoisomerase I. Here we show that cleavage and religation half-reactions of topoisomerase I are unaffected by PSF/p54(nrb), whereas the propensity of the enzyme to jump between separate DNA helices is stimulated. To demonstrate such an effect, topoisomerase I was first captured in suicidal cleavage of an oligonucleotide substrate. Subsequently, a cleavage/ligation equilibrium was established by adding a ligation donor under conditions allowing recleavage of the ligated substrate. Finally, a second oligonucleotide was added to the mixture, which also allowed suicidal cleavage by topoisomerase I, but did not accommodate the ligation donor of the first oligonucleotide. Thus, topoisomerase I was given the choice to engage in repeated cleavage/ligation cycles of the first oligonucleotide or to jump to the second suicide substrate and get trapped. PSF/p54(nrb) enhanced the cleavage rate of the second oligonucleotide (11-fold), suggesting that it stimulates the dissociation of topoisomerase I after ligation. Thus, stimulation of topoisomerase I catalysis by PSF/p54(nrb) seems to be affected by mobilization of the enzyme.
Straub
T
T
Department of Clinical Chemistry, University of Wuerzburg, Medical School, Germany.
Knudsen
B R
BR
Boege
F
F
D001483:Base Sequence; D002460:Cell Line; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004268:DNA-Binding Proteins; D006801:Humans; D007700:Kinetics; D034521:Nuclear Matrix-Associated Proteins; D009687:Nuclear Proteins / Q000378:metabolism*; D050810:Octamer Transcription Factors; D016601:RNA-Binding Proteins / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism
D004268:DNA-Binding Proteins; C083214:NONO protein, human; D034521:Nuclear Matrix-Associated Proteins; D009687:Nuclear Proteins; D050810:Octamer Transcription Factors; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; D004247:DNA; D004264:DNA Topoisomerases, Type I