Ty insertions upstream and downstream of native DUR1,2 promoter elements generate different patterns of DUR1,2 expression in Saccharomyces cerevisiae

Abstract

Expression of allantoin pathway genes is subject to induction and nitrogen catabolite repression. Two classes of cis-dominant mutations (DUR80 and DUR1,2-Oh) result in overproduction of DURI,2 mRNA. In DUR80 mutants, DURJ,2 expression remained inducible, nitrogen catabolite repression sensitive, and unresponsive to cell ploidy, i.e., overproduction was superimposed on normal gene regulation. DUR1,2-0h mutations, in contrast, generated a pattern of DUR1,2 expression similar to that often reported when a Ty element inserts upstream of a gene, the ROAM phenotype. We analyzed four independent DUR80 and DUR1,2-0h alleles. The DURJ,2-0Y mutation was, as expected, a Ty insertion at -445 3' of the native DUR1,2 upstream activation sequences (UASs). All three DUR80 alleles were also Ty insertions between -644 and -653 immediately 5' of the native DUR1,2 UASs. We suggest that the difference in DURJ,2-0h and DUR80 phenotypes depends on whether the native cis-acting elements and transcription factors associated with them can operate. If they can, enhancement of normally regulated DURJ,2 expression is observed. This is a novel phenotype for Ty insertions. If the native DURJ,2 cis-acting elements are not present, the case when Ty insertion occurs 3' of them, a ROAM phenotype is generated. Nitrogen-regulated upstream activation sequence (UASNTR)-homologous sequences present in the Ty 8 elements rather than cis-acting elements required for Ty transcription are the most likely candidates to serve as the cis-acting elements mediating the DUR80 phenotype.

Characteristic genome rearrangements in experimental evolution of Saccharomyces cerevisiae

“…In yeast, transposons have been observed to activate expression of nearby genes (e.g., ref. 33). CIT1 is one of the key regulated points in the tricarboxylic acid cycle (34).…”

Comparing whole genomes using DNA microarrays

“…of retrotransposons show substantial variation across strain backgrounds and species 74,75 , and novel transposon insertions can cause both adaptive 76,77 and detrimental 78 mutations. Retrotransposon proximity to genes can also modify gene expression and regulation 79 . Moreover, transposons are potentially a source of CNv as they are correlated with the breakpoints of genomic rearrangements from yeast 41,80 to humans 59 .…”