The Mute button: Turning down the volume of histone expression

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PROJECT SUMMARY During DNA replication, a cell must replicate not only its DNA, but also the nucleosomes that package its genome. To meet this extremely high demand for rapid histone protein biosynthesis, all eukaryotes coordinate high expression of replication-dependent (RD) histone gene clusters during S-phase of the cell division cycle. Regulating the level of expression of RD-histone genes during S-phase is important for maintaining genomic integrity and normal cell cycle progression, as too many or too few histones lead to toxic effects such as enhanced DNA damage sensitivity or cell cycle arrest. While the transcriptional activation of RD-histone genes has been characterized, little is known about the negative regulation that occurs as cells exit S-phase or the modulation of transcription that occurs during S-phase. My preliminary research has shown the Drosophila protein Mute (a homologue of human Yarp/Gon4L) is a prime candidate for a negative transcriptional regulator of RD-histone genes. I have found that loss of Mute uncouples expression of RD-histone genes from S-phase in Drosophila embryos. I hypothesize Mute is both restricting RD-histone expression to S-phase as well as regulating levels of expression during S- phase. This proposal seeks to uncover the mechanisms through which Mute represses RD- histone genes and how this repression is connected to the cell cycle. Using an interdisciplinary approach, the mechanisms of Mute’s repression at both the cellular and molecular levels will be explored using a combination of genomic, fluorescent imaging, genetic, and proteomic techniques in the Drosophila model system. This project will enhance our understanding of the role of histone gene regulation in metazoans and provide insight into the mechanisms that govern the regulation of this highly conserved cellular process.