Histone acetyl transferases (HATs) play a crucial role in eukaryotes by regulating chromatin architecture and locus-specific transcription. The GCN5 HAT was identified as a subunit of the SAGA (Spt-Ada-Gcn5-Acetyltransferase) multiprotein complex. Vertebrate cells express a second HAT, PCAF, that is 73% identical to GCN5. Here, we report the characterization of the mammalian ATAC (Ada-Two-A-Containing) complexes containing either GCN5 or PCAF in a mutually exclusive manner. In vitro ATAC complexes acetylate lysine 14 of histone H3. Moreover, ATAC- or SAGA-specific knock-down experiments suggest that both ATAC and SAGA are involved in the acetylation of histone H3K9 and K14 residues. Despite their catalytic similarities, SAGA and ATAC execute their coactivator functions on distinct sets of inducible target genes. Interestingly, ATAC strongly influences the global phosphorylation level of histone H3S10, suggesting that in mammalian cells a cross-talk exists linking ATAC function to H3S10 phosphorylation.

The centrosome functions as the main microtubule-organizing center of animal cells and is crucial for several fundamental cellular processes. Abnormalities in centrosome number and composition correlate with tumor progression and other diseases. Although proteomic studies have identified many centrosomal proteins, their interactions are incompletely characterized. The lack of information on the precise localization and interaction partners for many centrosomal proteins precludes comprehensive understanding of centrosome biology. Here, we utilize a combination of selective chemical crosslinking and superresolution microscopy to reveal novel functional interactions among a set of 31 centrosomal proteins. We reveal that Cep57, Cep63, and Cep152 are parts of a ring-like complex localizing around the proximal end of centrioles. Furthermore, we identify that STIL, together with HsSAS-6, resides at the proximal end of the procentriole, where the cartwheel is located. Our studies also reveal that the known interactors Cep152 and Plk4 reside in two separable structures, suggesting that the kinase Plk4 contacts its substrate Cep152 only transiently, at the centrosome or within the cytoplasm. Our findings provide novel insights into protein interactions critical for centrosome biology and establish a toolbox for future studies of centrosomal proteins.

HsSAS-6 homodimers are present in the cytoplasm and assemble into ninefold symmetrical arrays at centrosomes, thus initiating procentriole formation.

The regulation of autophagy in metazoans is only partly understood, and there is a need to identify the proteins that control this process. The diabetes-and obesity-regulated gene (DOR), a recently reported nuclear cofactor of thyroid hormone receptors, is expressed abundantly in metabolically active tissues such as muscle. Here, we show that DOR shuttles between the nucleus and the cytoplasm, depending on cellular stress conditions, and re-localizes to autophagosomes on autophagy activation. We demonstrate that DOR interacts physically with autophagic proteins Golgi-associated ATPase enhancer of 16 kDa (GATE16) and microtubule-associated protein 1A/1B-light chain 3. Gain-offunction and loss-of-function studies indicate that DOR stimulates autophagosome formation and accelerates the degradation of stable proteins. CG11347, the DOR Drosophila homologue, has been predicted to interact with the Drosophila Atg8 homologues, which suggests functional conservation in autophagy. Flies lacking CG11347 show reduced autophagy in the fat body during pupal development. All together, our data indicate that DOR regulates autophagosome formation and protein degradation in mammalian and Drosophila cells.