title: Transcriptional cosuppression of yeast Ty1 retrotransposons.
abstract: Cosuppression, the silencing of dispersed homologous genes triggered by high copy number, may have evolved in eukaryotic organisms to control molecular parasites such as viruses and transposons. Ty1 retrotransposons are dispersed gene repeats in Saccharomyces cerevisiae, where no cosuppression has been previously observed. Ty1 elements are seemingly expressed undeterred to a level as high as 10% of total mRNA. Using Ty1-URA3 reporters and negative selection with 5-fluoroorotic acid, it is shown that Ty1 genes can undergo transcriptional cosuppression that is independent of DNA methylation and polycomb-mediated repression. Expression of Ty1-related genes was shown to be in one of two states, the coexpressed state with all Ty1-related genes transcribed or the cosuppressed state with all Ty1-related genes shut off, without uncoordinated or mosaic expression in any individual cell. Rapid switches between the two states were observed. A high copy number of Ty1 elements was shown to be required for the initiation of Ty1 homology-dependent gene silencing, implying that Ty1 gene expression is under negative feedback control. Ty1 transcriptional repressors facilitated the onset of Ty1 cosuppression, and the native Ty1 promoters were required for Ty1 cosuppression, indicating that Ty1 cosuppression occurs at the transcriptional level.
authors.affiliation: Department of Medical Biochemistry and Genetics, Texas A&M University System Health Science Center, College Station, Texas 77843-1114, USA. ywjiang@medicine.tamu.edu
authors.forename: Yi Wei
authors.initials: YW
authors.lastname: Jiang
mesh_terms: D001483:Base Sequence; D002843:Chromatin / Q000235:genetics / Q000378:metabolism; D015825:Chromosomes, Fungal / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation; D005246:Feedback; D005656:Fungal Proteins / Q000096:biosynthesis / Q000235:genetics; D015966:Gene Expression Regulation, Fungal; D020868:Gene Silencing; D017930:Genes, Reporter; D008969:Molecular Sequence Data; D009963:Orotic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics; D018626:Retroelements / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D012641:Selection, Genetic; D012689:Sequence Homology, Nucleic Acid; D020079:Terminal Repeat Sequences; D014158:Transcription, Genetic
chemical_list: D002843:Chromatin; D005656:Fungal Proteins; D011993:Recombinant Fusion Proteins; D018626:Retroelements; D009963:Orotic Acid; C001242:5-fluoroorotic acid