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Eukaryotic organisms utilize post-translational modifications of highly conserved histone proteins to control gene expression programs. Methylation of lysine 4 on histone H3 (H3K4me) in particular, is thought to be associated with actively transcribed DNA. Paradoxically, recent evidence has suggested that H3K4me has a repressive function as well. Pho23, a member of the highly conserved ING family of tumour suppressor proteins, binds H3K4me and is a component of the gene repressive complex, Rpd3L. My genetic analysis suggests that Pho23 controls transcriptional repression via H3K4me and that Pho23 is itself regulated by the sequence-specific DNA-binding protein Ume6. Moreover, this Ume6-regulated function appears to be governed by Ume6 phosphorylation by Mck1, an evolutionarily conserved kinase. Finally, while Ume6/Pho23 are known to function together with the histone deacteylase Rpd3, my findings suggest the existence of an Rpd3-independent function for Pho23.

Eukaryotic organisms utilize post-translational modifications of highly conserved histone proteins to control gene expression programs. Methylation of lysine 4 on histone H3 (H3K4me) in particular, is thought to be associated with actively transcribed DNA. Paradoxically, recent evidence has suggested that H3K4me has a repressive function as well. Pho23, a member of the highly conserved ING family of tumour suppressor proteins, binds H3K4me and is a component of the gene repressive complex, Rpd3L. My genetic analysis suggests that Pho23 controls transcriptional repression via H3K4me and that Pho23 is itself regulated by the sequence-specific DNA-binding protein Ume6. Moreover, this Ume6-regulated function appears to be governed by Ume6 phosphorylation by Mck1, an evolutionarily conserved kinase. Finally, while Ume6/Pho23 are known to function together with the histone deacteylase Rpd3, my findings suggest the existence of an Rpd3-independent function for Pho23.