The fission yeast spindle pole body (SPB) is a nucleus-associated organelle that duplicates once each cell cycle during interphase. Duplicated SPBs serve as the poles of an intranuclear mitotic spindle after their insertion into the nuclear envelope in mitosis (Ding et al., Mol. Biol. Cell 8, 1461-1479. Here, we report the identification and characterization of Schizosaccharomyces pombe cdc31p, a member of the conserved calcium-binding centrin/CDC31 family. Immunofluorescence and immunoelectron microscopy show that cdc31p is a SPB component localized at the halfbridge structure of the SPB. cdc31 is an essential gene and ⌬cdc31 cells and cdc31 conditional mutant cells arrest in mitosis with a monopolar mitotic spindle organized from a single SPB. EM analysis demonstrates that mutant cdc31 cells fail to duplicate the SPB. In addition, cdc31p exhibits genetic interactions with the SPB component sad1p and is required for sad1p localization. Finally, cdc31 mutant can undergo single or multiple rounds of septation before the exit from mitosis, suggesting that cdc31p activity or SPB duplication may be required for the proper coordination between the exit from mitosis and the initiation of septation.
Diverse guanine nucleotide exchange factors (GEFs) regulate the activity of GTP binding proteins. One of the most complicated pairs is eukaryotic initiation factor 2B (eIF2B) and eIF2, which function during protein synthesis initiation in eukaryotes. We have mutated conserved surface residues within the eIF2B GEF domain, located at the eIF2B C terminus. Extensive genetic and biochemical characterization established how these residues contribute to GEF activity. We find that the universally conserved residue E569 is critical for activity and that even a conservative E569D substitution is lethal in vivo. Several mutations within residues close to E569 have no discernible effect on growth or GCN4 expression, but an alanine substitution at the adjacent L568 is cold sensitive and deregulates GCN4 activity at 15°C. The mutation of W699, found on a separate surface approximately 40 Å from E569, is also lethal. Binding studies show that W699 is critical for interaction with eIF2, while L568 and E569 are not. In contrast, all three residues are critical for interaction with eIF2␥. These data show that multiple contacts between eIF2␥ and eIF2B mediate nucleotide exchange.The cap-dependent pathway for the initiation of translation requires the assembly of eukaryotic initiation factor (eIF) ribosomal subunits and a selected mRNA. Central to the initiation process is the GTP binding protein eIF2, which delivers aminoacylated initiator methionyl tRNA (Met-tRNA i Met ) to the 40S ribosome as part of a multifactor complex containing eIFs 1, 3, and 5 (5). This 43S preinitiation complex associates with the 5Ј end of an mRNA and migrates along it to locate an AUG initiator codon with the aid of other factors. AUG codon recognition, eIF5-promoted hydrolysis of GTP bound to eIF2, and phosphate release stimulate eIF2-GDP and eIF5 dissociation from the initiation complex, probably as an eIF2-GDP/ eIF5 complex (33). Met-tRNA i Met remains bound to the 40S ribosomal subunit at the AUG and is probably stabilized by eIF1A/eIF5B-GTP. 60S ribosomal subunit joining is accelerated by GTP hydrolysis and the release of eIF5B-GDP. At this point, translation elongation can commence (20).The regeneration of eIF2-GTP from the inactive GDPbound complex released from the initiation complex is carried out by the guanine nucleotide exchange factor (GEF) eIF2B. eIF2B accelerates the otherwise slow dissociation of GDP from eIF2, allowing its replacement with GTP. This process is regulated by the phosphorylation of eIF2␣ on the conserved ser51 residue in response to a diverse set of cellular stresses (20). For example, in yeast cells (Saccharomyces cerevisiae), translational control of GCN4 expression proceeds by the following pathway: amino acid starvation activates Gcn2p, which phosphorylates eIF2␣ and inhibits eIF2B activity. This lowers the rate of nucleotide exchange and slows recruitment of the eIF2-GTP/Met-tRNA i Met ternary complex (TC) to mRNAs. GCN4 translation is activated by this response, as it contains short upstream open reading frames tha...
Polyadenylation is a co-transcriptional process that modifies mRNA 3′-ends in eukaryotes. In yeast, CF IA and CPF constitute the core 3′-end maturation complex. CF IA comprises Rna14p, Rna15p, Pcf11p and Clp1p. CF IA interacts with the C-terminal domain of RNA Pol II largest subunit via Pcf11p which links pre-mRNA 3′-end processing to transcription termination. Here, we analysed the role of Clp1p in 3′ processing. Clp1p binds ATP and interacts in CF IA with Pcf11p only. Depletion of Clp1p abolishes transcription termination. Moreover, we found that association of mutations in the ATP-binding domain and in the distant Pcf11p-binding region impair 3′-end processing. Strikingly, these mutations prevent not only Clp1p-Pcf11p interaction but also association of Pcf11p with Rna14p-Rna15p. ChIP experiments showed that Rna15p cross-linking to the 3′-end of a protein-coding gene is perturbed by these mutations whereas Pcf11p is only partially affected. Our study reveals an essential role of Clp1p in CF IA organization. We postulate that Clp1p transmits conformational changes to RNA Pol II through Pcf11p to couple transcription termination and 3′-end processing. These rearrangements likely rely on the correct orientation of ATP within Clp1p.
These first encouraging safety results do support further development of EHT0202 in order to assess its clinical efficacy and to confirm its tolerability in a larger cohort of Alzheimer patients and for a longer period.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.