Structures of naturally evolved CUP1 tandem arrays in yeast indicate that these arrays are generated by unequal nonhomologous recombination.
Bottom Line: In the yeast Saccharomyces cerevisiae, most strains contain tandemly duplicated copies of CUP1, a gene that encodes a copper-binding metallothionein.By screening 101 natural isolates of S. cerevisiae, we identified five different types of CUP1-containing repeats, as well as strains that only had one copy of CUP1.A comparison of the DNA sequences of these strains indicates that the CUP1 tandem arrays were generated by unequal nonhomologous recombination events from strains that had one CUP1 gene.
Affiliation: Department of Molecular Genetics and Microbiology and University Program in Genetics and Genomics, Duke University Medical Center, Durham, North Carolina 27710.Show MeSH
Mentions: All five classes of repeats can be explained by the duplication mechanism shown in Figure 8. We suggest that, during replication of a chromosome with only one copy of CUP1, two breaks occur, one centromere-distal and one centromere-proximal to the CUP1 locus. The joining of these broken ends by nonhomologous end-joining results in two products, one with a CUP1 deletion and one with a tandem duplication. An alternative possibility is that the repeats were generated by a single break in the centromere-distal location, followed by a BIR event in which the centromere-proximal site was invaded. Because most BIR events involve either extensive sequence homology (Paques and Haber 1999) or 5−20 bp of microhomology (Payen et al. 2008), and most of the observed breakpoints in our study have very little or no homology, we favor the first alternative.
Affiliation: Department of Molecular Genetics and Microbiology and University Program in Genetics and Genomics, Duke University Medical Center, Durham, North Carolina 27710.