A Yeast Catabolic Enzyme Controls Transcriptional Memory

• Published in: Current biology Vol. 17; no. 23; pp. 2041 - 2046
• Main Authors: Zacharioudakis, Ioannis, Gligoris, Thomas, Tzamarias, Dimitris
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 04.12.2007
• Subjects: Culture Media; DNA; Galactokinase - genetics; Galactokinase - metabolism; Galactose - metabolism; Gene Deletion; Gene Expression Regulation, Fungal; Glucose - metabolism; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - growth & development; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; Signal Transduction; SIGNALING; Transcription Factors - genetics; Transcription Factors - metabolism; Transcription, Genetic; DNA; SIGNALING
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2007.10.044

It has been postulated that chromatin modifications can persist through mitosis and meiosis, thereby securing memory of transcriptional states [1–4]. Whether these chromatin marks can self-propagate in progeny independently of relevant trans-acting factors is an important question in phenomena related to epigenesis. “Adaptive cellular memory” displayed by yeast cells offers a convenient system to address this question. The yeast GAL genes are slowly activated by Gal4 when cells are first exposed to galactose, but their progeny, grown in glucose media, exhibit a fast activation mode upon re-exposure to this sugar [5]. This “galactose memory” persists for several generations and was recently proposed to involve chromatin modifications and perinuclear topology of the GAL genes cluster [5, 6]. Here, we perform a heterokaryon assay demonstrating that this memory does not have a chromatin basis but is maintained by cytoplasmic factor(s) produced upon previous galactose induction. We show that Gal3, the cytoplasmic rate-limiting factor that releases the Gal4 activator, is dispensable for preserving galactose memory. Instead, the important memory determinant is a close Gal3 homolog, the highly expressed Gal1 galactokinase, the residual activity of which preserves memory in progeny cells by rapidly turning on the Gal4 activator upon cells' re-exposure to galactose.