The yeast NuA4 and Drosophila MSL complexes contain homologous subunits important for transcription regulation.
ABSTRACT In Drosophila, the MSL complex is required for the dosage compensation of X-linked genes in males and contains a histone acetyltransferase, MOF. A point mutation in the MOF acetyl-CoA-binding site results in male-specific lethality. Yeast Esa1p, a MOF homolog, is essential for cell cycle progression and is the catalytic subunit of the NuA4 acetyltransferase complex. Here we report that NuA4 purified from yeast with a point mutation in the acetyl-CoA-binding domain of Esa1p exhibits a strong decrease in histone acetyltransferase activity, yet has no effect on growth. We demonstrate that Eaf3p (Esa1p-associated factor-3 protein), a yeast protein homologous to the Drosophila dosage compensation protein MSL3, is also a stable component of the NuA4 complex. Unlike other subunits of the complex, it is not essential, and the deletion mutant has no growth phenotype. NuA4 purified from the mutant strain has a decreased apparent molecular mass, but retains wild-type levels of histone H4 acetyltransferase activity. The EAF3 deletion and the ESA1 mutation lead to a decrease in PHO5 gene expression; the EAF3 deletion also significantly reduces HIS4 and TRP4 expressions. These results, together with those previously obtained with both the MSL and NuA4 complexes, underscore the importance of targeted histone H4 acetylation for the gene-specific activation of transcription.
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ABSTRACT: The level of stem cell proliferation must be tightly controlled for proper development and tissue homeostasis. Multiple levels of gene regulation are often employed to regulate stem cell proliferation to ensure that the amount of proliferation is aligned with the needs of the tissue. Here we focus on proteasome-mediated protein degradation as a means of regulating the activities of proteins involved in controlling the stem cell proliferative fate in the C. elegans germ line. We identify five potential E3 ubiquitin ligases, including the RFP-1 RING finger protein, as being involved in regulating proliferative fate. RFP-1 binds to MRG-1, a homologue of the mammalian chromodomain-containing protein MRG15 (MORF4L1), which has been implicated in promoting the proliferation of neural precursor cells. We find that C. elegans with reduced proteasome activity, or that lack RFP-1 expression, have increased levels of MRG-1 and a shift towards increased proliferation in sensitized genetic backgrounds. Likewise, reduction of MRG-1 partially suppresses stem cell overproliferation. MRG-1 levels are controlled independently of the spatially regulated GLP-1/Notch signalling pathway, which is the primary signal controlling the extent of stem cell proliferation in the C. elegans germ line. We propose a model in which MRG-1 levels are controlled, at least in part, by the proteasome, and that the levels of MRG-1 set a threshold upon which other spatially regulated factors act in order to control the balance between the proliferative fate and differentiation in the C. elegans germ line. © 2015. Published by The Company of Biologists Ltd.Development 01/2015; 142(2):291-302. DOI:10.1242/dev.115147 · 6.27 Impact Factor