Site-specific in vivo cleavages by DNA topoisomerase I in the regulatory regions of the 35 S rRNA in Saccharomyces cerevisiae are transcription independent.
Eukaryotic type I DNA topoisomerase controls DNA topology by transiently breaking and resealing one strand of DNA at a time. During transcription and replication its action reduces the torsional stress derived from these activities. The association of DNA topoisomerase I with the nucleolus has been reported and this enzyme was shown to be involved in yeast rDNA metabolism. Here, we have investigated the in vivo presence of DNA topoisomerase I cleavage sites in the non-transcribed spacer of the rDNA cluster. We show a specific profile of highly localized cleavage in relevant areas of this region. The sites are detected in the promoter and in the enhancer regions of the 35 S gene. The analysis of mutants in which transcription is prevented and/or reduced, namely a strain lacking the 43 kDa subunit of RNA polymerase I, a second one that does note transcribe, lacking a subunit of the core factor and another member of the RNA polymerase I transcription factors lacking one of the UAF component which transcribes at very low level, show that DNA topoisomerase I cleavage sites are not related to transcription by RNA polymerase I. These findings point to a role for DNA topoisomerase I that is additional to the commonly recognized function in removing the transcription-induced topological stress.
Vogelauer
M
M
Dipartimento di Genetica e Biologia Molecolare, Università di Roma "La Sapienza", Rome, 00185, Italy.
Camilloni
G
G
D002166:Camptothecin / Q000494:pharmacology; D002874:Chromosome Mapping; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004275:DNA, Ribosomal / Q000235:genetics; D004742:Enhancer Elements, Genetic / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D009154:Mutation; D012318:RNA Polymerase I / Q000235:genetics; D012335:RNA, Ribosomal / Q000235:genetics; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D014158:Transcription, Genetic / Q000235:genetics*
D004275:DNA, Ribosomal; D004791:Enzyme Inhibitors; D012335:RNA, Ribosomal; D012318:RNA Polymerase I; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin