In the IMD2 gene of Saccharomyces cerevisiae , the expression memory suppresses the induction of expression during GTP depletion

In budding yeast, genes located within the heterochromatin regions are transcriptionally repressed. The boundaries of heterochromatin regions fluctuate in response to intracellular and extracellular influences, thereby altering the gene expression in nearby regions. However, the mechanisms regulating chromatin organization at specific loci are unclear. Therefore, we used a single-cell tracking system to analyse IMD2, a gene located in the subtelomeric regions, whose expression is regulated by variations in heterochromatin structure. While the heterochromatin region at the IMD2 locus fluctuates to induce expression in response to GTP depletion, we found that IMD2 expression states change independently of GTP levels in a subset of cells. When the IMD2 expression state was tracked before and after GTP depletion, cells that had previously exhibited IMD2 expression were less likely to show fluctuations in heterochromatin state following GTP depletion. These results suggest that the heterogeneous regulation of IMD2 expression observed at the cell population level is influenced by prior transcriptional experience, which is associated with variations in the heterochromatin structure.