Biomaterial Database

A subthreshold level of DNA topoisomerases leads to the excision of yeast rDNA as extrachromosomal rings. 1989

R A Kim, and J C Wang

Department of Biochemistry and Molecular Biology, Harvard University, Cambridge, Massachusetts 02138.

In a yeast DNA topoisomerase double mutant TG205 (delta top1 top2-4), over half of the rDNA is present as extrachromosomal rings containing one 9 kb unit of the rDNA gene or tandem repeats of it. Expression of a plasmid-borne TOP1 or TOP2 gene in the strain leads to the integation of the extrachromosomal rDNA rings back into the chromosomal rDNA cluster. When the plasmid-borne topoisomerase gene is expressed from an inducible promoter of the GAL1 gene, repression of the gene by dextrose leads to reappearance of the extrachromosomal rDNA rings. The DNA topoisomerase-dependent excision/integration of rDNA is discussed in terms of the possibility of rDNA supercoiling by transcription and the effects of DNA topology on intra- and interchromosomal recombination.

UI	MeSH Term	Description	Entries
D009154	Mutation	Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.	Mutations
D011995	Recombination, Genetic	Production of new arrangements of DNA by various mechanisms such as assortment and segregation, CROSSING OVER; GENE CONVERSION; GENETIC TRANSFORMATION; GENETIC CONJUGATION; GENETIC TRANSDUCTION; or mixed infection of viruses.	Genetic Recombination,Recombination,Genetic Recombinations,Recombinations,Recombinations, Genetic
D004264	DNA Topoisomerases, Type I	DNA TOPOISOMERASES that catalyze ATP-independent breakage of one of the two strands of DNA, passage of the unbroken strand through the break, and rejoining of the broken strand. DNA Topoisomerases, Type I enzymes reduce the topological stress in the DNA structure by relaxing the superhelical turns and knotted rings in the DNA helix.	DNA Nicking-Closing Protein,DNA Relaxing Enzyme,DNA Relaxing Protein,DNA Topoisomerase,DNA Topoisomerase I,DNA Topoisomerase III,DNA Topoisomerase III alpha,DNA Topoisomerase III beta,DNA Untwisting Enzyme,DNA Untwisting Protein,TOP3 Topoisomerase,TOP3alpha,TOPO IIIalpha,Topo III,Topoisomerase III,Topoisomerase III beta,Topoisomerase IIIalpha,Topoisomerase IIIbeta,DNA Nicking-Closing Proteins,DNA Relaxing Enzymes,DNA Type 1 Topoisomerase,DNA Untwisting Enzymes,DNA Untwisting Proteins,Topoisomerase I,Type I DNA Topoisomerase,III beta, Topoisomerase,III, DNA Topoisomerase,III, Topo,III, Topoisomerase,IIIalpha, TOPO,IIIalpha, Topoisomerase,IIIbeta, Topoisomerase,Topoisomerase III, DNA,Topoisomerase, TOP3,beta, Topoisomerase III
D004270	DNA, Circular	Any of the covalently closed DNA molecules found in bacteria, many viruses, mitochondria, plastids, and plasmids. Small, polydisperse circular DNA's have also been observed in a number of eukaryotic organisms and are suggested to have homology with chromosomal DNA and the capacity to be inserted into, and excised from, chromosomal DNA. It is a fragment of DNA formed by a process of looping out and deletion, containing a constant region of the mu heavy chain and the 3'-part of the mu switch region. Circular DNA is a normal product of rearrangement among gene segments encoding the variable regions of immunoglobulin light and heavy chains, as well as the T-cell receptor. (Riger et al., Glossary of Genetics, 5th ed & Segen, Dictionary of Modern Medicine, 1992)	Circular DNA,Circular DNAs,DNAs, Circular
D004271	DNA, Fungal	Deoxyribonucleic acid that makes up the genetic material of fungi.	Fungal DNA
D004275	DNA, Ribosomal	DNA sequences encoding RIBOSOMAL RNA and the segments of DNA separating the individual ribosomal RNA genes, referred to as RIBOSOMAL SPACER DNA.	Ribosomal DNA,rDNA
D004278	DNA, Superhelical	Circular duplex DNA isolated from viruses, bacteria and mitochondria in supercoiled or supertwisted form. This superhelical DNA is endowed with free energy. During transcription, the magnitude of RNA initiation is proportional to the DNA superhelicity.	DNA, Supercoiled,DNA, Supertwisted,Supercoiled DNA,Superhelical DNA,Supertwisted DNA
D005111	Extrachromosomal Inheritance	Vertical transmission of hereditary characters by DNA from cytoplasmic organelles such as MITOCHONDRIA; CHLOROPLASTS; and PLASTIDS, or from PLASMIDS or viral episomal DNA.	Cytoplasmic Inheritance,Extranuclear Inheritance,Inheritance, Cytoplasmic,Inheritance, Extrachromosomal,Inheritance, Extranuclear
D005786	Gene Expression Regulation	Any of the processes by which nuclear, cytoplasmic, or intercellular factors influence the differential control (induction or repression) of gene action at the level of transcription or translation.	Gene Action Regulation,Regulation of Gene Expression,Expression Regulation, Gene,Regulation, Gene Action,Regulation, Gene Expression
D012441	Saccharomyces cerevisiae	A species of the genus SACCHAROMYCES, family Saccharomycetaceae, order Saccharomycetales, known as "baker's" or "brewer's" yeast. The dried form is used as a dietary supplement.	Baker's Yeast,Brewer's Yeast,Candida robusta,S. cerevisiae,Saccharomyces capensis,Saccharomyces italicus,Saccharomyces oviformis,Saccharomyces uvarum var. melibiosus,Yeast, Baker's,Yeast, Brewer's,Baker Yeast,S cerevisiae,Baker's Yeasts,Yeast, Baker