Identification of autonomously replicating circular subtelomeric Y' elements in Saccharomyces cerevisiae.
We marked a large number of yeast telomeres within their Y' regions by transforming strains with a fragment of Y' DNA into which the URA3 gene had been inserted. A few of the Ura+ transformants obtained were very unstable and were found to contain autonomously replicating URA3-marked circular Y' elements in high copy number. These marked extrachromosomal circles were capable of reintegrating into the chromosome at other telomeric locations. In contrast, most of the Ura+ transformants obtained were quite stable mitotically and were marked at bona fide chromosomal ends. These stable transformants gave rise to mitotically unstable URA3-marked circular Y' elements at a low frequency (up to 2.5%). The likelihood that such excisions and integrations represent a natural process in Saccharomyces cerevisiae is supported by our identification of putative Y' circles in untransformed strains. The transfer of Y' information among telomeres via a circular intermediate may be important for homogenizing the sequences at the ends of yeast chromosomes and for generating the frequent telomeric rearrangements that have been observed in S. cerevisiae.
D002875:Chromosomes / Q000648:ultrastructure; D004261:DNA Replication; D004270:DNA, Circular / Q000235:genetics; D004271:DNA, Fungal / Q000235:genetics; D005111:Extrachromosomal Inheritance; D008540:Meiosis; D008938:Mitosis; D012093:Replicon; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D014170:Transformation, Genetic
D004270:DNA, Circular; D004271:DNA, Fungal