Nitrogen starvation and chromatin dynamics: The role of Gcn5 in glycogen metabolism

Glycogen metabolism is a crucial process in Saccharomyces cerevisiae, enabling energy storage and adaptation to changing environmental conditions. Histone acetyltransferase Gcn5, a key component of the SAGA complex, is known to regulate gene expression through chromatin remodeling. This study investigates the role of Gcn5 in modulating glycogen metabolism under normal and nitrogen-starvation conditions. Gcn5 deletion significantly impairs yeast growth, as evidenced by slower doubling times and reduced specific growth rates, highlighting its role in metabolic adaptation. Glycogen accumulation assays revealed that gcn5Δ mutants accumulate more glycogen during the exponential growth phase compared to wild-type cells, suggesting that Gcn5 maintains basal glycogen levels by regulating genes involved in glycogen synthesis and degradation. However, under nitrogen starvation, gcn5Δ mutants exhibit drastically reduced glycogen accumulation, indicating that Gcn5 is critical for stress-responsive metabolic reprogramming. Promoter analyses of genes involved in glycogen metabolism identified overlaps between nucleosome positions and Msn2/4 transcription factor binding sites. These findings suggest that Gcn5-mediated nucleosome mobilization enables Msn2/4 binding and transcriptional activation of stress-responsive genes. The impaired glycogen storage in gcn5Δ mutants under nitrogen starvation underscores the essential role of Gcn5 in coordinating chromatin remodeling and transcriptional regulation during environmental stress. Overall, this study highlights the central role of Gcn5 in balancing glycogen metabolism and cellular adaptation, providing insights into its broader regulatory functions in yeast stress responses.