RESUMO
RCC1 associates to chromatin dynamically within mitosis and catalyzes Ran-GTP production. Exogenous RCC1 disrupts kinetochore structure in Xenopus egg extracts (XEEs), but the molecular basis of this disruption remains unknown. We have investigated this question, utilizing replicated chromosomes that possess paired sister kinetochores. We find that exogenous RCC1 evicts a specific subset of inner KT proteins including Shugoshin-1 (Sgo1) and the chromosome passenger complex (CPC). We generated RCC1 mutants that separate its enzymatic activity and chromatin binding. Strikingly, Sgo1 and CPC eviction depended only on RCC1's chromatin affinity but not its capacity to produce Ran-GTP. RCC1 similarly released Sgo1 and CPC from synthetic kinetochores assembled on CENP-A nucleosome arrays. Together, our findings indicate RCC1 regulates kinetochores at the metaphase-anaphase transition through Ran-GTP-independent displacement of Sgo1 and CPC.
Assuntos
Proteínas de Ciclo Celular/metabolismo , Fatores de Troca do Nucleotídeo Guanina/metabolismo , Proteínas Nucleares/metabolismo , Proteínas de Xenopus/metabolismo , Xenopus laevis/metabolismo , Proteína ran de Ligação ao GTP/metabolismo , Animais , Proteínas de Ciclo Celular/genética , Centrômero/metabolismo , Proteína Centromérica A/metabolismo , Cromatina/metabolismo , Fatores de Troca do Nucleotídeo Guanina/genética , Humanos , Cinetocoros/metabolismo , Mitose , Mutagênese Sítio-Dirigida , Proteínas Nucleares/genética , Óvulo/metabolismoRESUMO
The phosphorylation of threonine residues in proteins regulates diverse processes in eukaryotic cells, and thousands of threonine phosphorylations have been identified. An understanding of how threonine phosphorylation regulates biological function will be accelerated by general methods to biosynthesize defined phosphoproteins. Here we describe a rapid approach for directly discovering aminoacyl-tRNA synthetase-tRNA pairs that selectively incorporate non-natural amino acids into proteins; our method uses parallel positive selections combined with deep sequencing and statistical analysis and enables the direct, scalable discovery of aminoacyl-tRNA synthetase-tRNA pairs with mutually orthogonal substrate specificity. By combining a method to biosynthesize phosphothreonine in cells with this selection approach, we discover a phosphothreonyl-tRNA synthetase-tRNACUA pair and create an entirely biosynthetic route to incorporating phosphothreonine in proteins. We biosynthesize several phosphoproteins and demonstrate phosphoprotein structure determination and synthetic protein kinase activation.
Assuntos
Escherichia coli/metabolismo , Fosfotreonina/metabolismo , Aminoacil-tRNA Sintetases/genética , Aminoacil-tRNA Sintetases/metabolismo , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Escherichia coli/genética , Engenharia Genética , Modelos Moleculares , Conformação Proteica , Engenharia de Proteínas , Processamento de Proteína Pós-Traducional , RNA de Transferência/genética , RNA de Transferência/metabolismo , Salmonella enterica/metabolismo , Especificidade por SubstratoRESUMO
Accurate control of the Ras-related nuclear protein (Ran) GTPase cycle depends on the regulated activity of regulator of chromosome condensation 1 (RCC1), Ran's nucleotide exchange factor. RanBP1 has been characterized as a coactivator of the Ran GTPase-activating protein RanGAP1. RanBP1 can also form a stable complex with Ran and RCC1, although the dynamics and function of this complex remain poorly understood. Here, we show that formation of the heterotrimeric RCC1/Ran/RanBP1 complex in M phase Xenopus egg extracts controls both RCC1's enzymatic activity and partitioning between the chromatin-bound and soluble pools of RCC1. This mechanism is critical for spatial control of Ran-guanosine triphosphate (GTP) gradients that guide mitotic spindle assembly. Moreover, phosphorylation of RanBP1 drives changes in the dynamics of chromatin-bound RCC1 pools at the metaphase-anaphase transition. Our findings reveal an important mitotic role for RanBP1, controlling the spatial distribution and magnitude of mitotic Ran-GTP production and thereby ensuring accurate execution of Ran-dependent mitotic events.
