Time-Dependent Nucleosome Remodeling During Galactose-Induced Ty1 Expression in Saccharomyces cerevisiae

ABSTRACT: The relationship between chromatin structure and transposable element (TE) integration is a fundamental question as nucleosomes can either mediate or inhibit TE insertion. The Ty1 element in Saccharomyces cerevisiae preferentially inserts upstream of RNA Polymerase III-transcribed genes, in a manner coincident with nucleosome positioning. Ty1 insertion positions have largely been inferred from nucleosome occupancy maps, but this approach is imperfect. Nucleosome occupancy maps are typically generated from wild-type Saccharomyces cerevisiae cells grown in standard conditions. Many Ty1 studies rely on a galactose-inducible expression system and it is not yet known if Ty1 overexpression from the GAL1 promoter itself alters nucleosome organization under inducing conditions. Here, we used a galactose-inducible Ty1 expression system and genome-wide MNase-seq to determine whether Ty1 donor plasmid transformation and overexpression alter nucleosome occupancy. We find that changes in carbon source do not substantially alter genome-wide nucleosome organization. In contrast, galactose induction of Ty1 expression revealed time-dependent changes in nucleosome occupancy. Nucleosome organization is unchanged across pre-induction, 6-hour galactose exposure, and post-induction repressing conditions, but nucleosome occupancy shifted at 12 and 24 hours, with changes evident at both Pol II and tRNA genes. We also found that Ty1 integration events are rare at early time points, emerge by 12 hours, and accumulate substantially by 24 hours. Ty1 preferentially targets nucleosomal DNA, but prolonged induction shifts insertion positions relative to nucleosomes. We also find that Ty1 preferentially targets nucleosomal DNA that lies in close proximity to histones, with this preference showing time-dependent shifts during induction.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE337686 | GEO | 2026/07/29

REPOSITORIES: GEO