Project description:SDS22 forms an inactive complex with nascent protein phosphatase-1 (PP1) and Inhibitor-3 (I3). SDS22:PP1:I3 is a substrate for the ATPase p97/VCP, which liberates PP1 for binding to canonical regulatory subunits. The exact role of SDS22 in PP1-holoenzyme assembly remains elusive. Here, we show that SDS22 prevents the aggregation of nascent PP1. In the absence of SDS22, PP1 was gradually lost, resulting in substrate hyperphosphorylation and a proliferation arrest. A human patient with an unstable SDS22 mutant also expressed reduced levels of PP1 and suffered from neurodevelopmental retardation. We furthermore found that SDS22 directly binds to I3 and that this is essential for the stable assembly of SDS22:PP1:I3, the recruitment of p97/VCP, and the extraction of SDS22 during holoenzyme assembly. SDS22 with a disabled I3-binding site co-transfered with PP1 to canonical regulatory subunits, thereby forming non-functional holoenzymes. Our data show that SDS22, by its ability to bind to both PP1 and I3, integrates the major steps of PP1 holoenzyme assembly.
Project description:Accurate assembly of newly- synthesized proteins into functional oligomers is crucial for cell activity. In this study, we investigated whether direct interaction of two nascent proteins, emerging from nearby ribosomes (co-co assembly), constitutes a general mechanism for oligomer formation. We used a proteome-wide screen to detect nascent chain-connected ribosome pairs and identified hundreds of homomer subunits that co-co assemble in human cells. Interactions are mediated by five major domain classes, among which N-terminal coiled coils are the most prevalent. We were able to reconstitute co-co assembly of nuclear lamin in Escherichia coli, demonstrating that dimer formation is independent of dedicated assembly machineries. Co-co assembly may thus represent an efficient way to limit protein aggregation risks posed by diffusion-driven assembly routes and ensure isoform-specific homomer formation.
Project description:Folding of newly synthesized proteins to the native state is a major challenge within the crowded cellular environment, since non-productive interactions can lead to misfolding, aggregation and degradation1. Cells cope with this challenge by coupling synthesis with polypeptide folding and by employing molecular chaperones to safeguard folding already cotranslationally2. However, little is known about the final step of folding, the assembly of polypeptides into complexes, although most of the cellular proteome forms oligomeric assemblies3. In prokaryotes, a proof-of-concept study showed that assembly of heterodimeric luciferase is an organized cotranslational process, facilitated by spatially confined translation of the subunits encoded on a polycistronic mRNA4. In eukaryotes, however, fundamental differences such as rarity of polycistronic mRNAs and different chaperone constellations raise the question whether assembly is also coordinated with translation. Here we provide a systematic and mechanistic analysis of protein complex assembly in eukaryotes using ribosome profiling. We determined the in vivo nascent subunits interactions of 12 hetero-oligomeric protein complexes of Saccharomyces cerevisiae at near-residue resolution. We find 9 complexes assemble cotranslationally; the 3 complexes that do not show cotranslational interactions are regulated by dedicated assembly chaperones5-7. Cotranslational assembly often occurs uni-directionally, with one fully synthesized subunit engaging its nascent partner subunit(s), thereby counteracting its aggregation propensity. The onset of cotranslational subunit association coincides sharply with full exposure of the nascent interaction domain at the ribosomal tunnel exit. The action of the ribosome-associated Hsp70 chaperone Ssb8 is coordinated with assembly. Ssb transiently engages partially synthesized interaction domains, then dissociates before the onset of partner subunit association, presumably to prevent premature assembly interactions. Our study shows that cotranslational subunit association is a prevalent mechanism for hetero-oligomers assembly in yeast and indicates that translation, folding and assembly of protein complexes are integrated processes in eukaryotes.
Project description:Deregulated expression of MYC induces a dependence on the NUAK1 kinase, but the molecular mechanisms underlying this dependence have not been fully clarified. Here we show that NUAK1 is a predominantly nuclear protein that associates with a network of nuclear protein phosphatase 1 (PP1) interactors and that PNUTS, a nuclear regulatory subunit of PP1, is phosphorylated by NUAK1. Both NUAK1 and PNUTS associate with the splicing machinery. Inhibition of NUAK1 abolishes chromatin association of PNUTS, reduces spliceosome activity and suppresses nascent RNA synthesis. Activation of MYC does not bypass the requirement for NUAK1 for spliceosome activity, but significantly attenuates transcription inhibition. Consequently, NUAK1 inhibition in MYC-transformed cells induces global accumulation of RNAPII both at the pause-site and at the first exon/intron boundary, but does not increase mRNA synthesis. We suggest that NUAK1 inhibition in the presence of deregulated MYC traps non-productive RNAPII due to the absence of correctly assembled spliceosomes.
Project description:Molecular functions of the Nucleosome Remodeling and Deacetylation (NuRD) complex in the control of gene expression were investigated using an inducible system to direct its assembly in embryonic stem cells. This dataset profiles nascent RNA transcription in response to NuRD induction.