Dataset Information

The Dedicated Chaperone Acl4 Escorts Ribosomal Protein Rpl4 to Its Nuclear Pre-60S Assembly Site.

ABSTRACT: Ribosomes are the highly complex macromolecular assemblies dedicated to the synthesis of all cellular proteins from mRNA templates. The main principles underlying the making of ribosomes are conserved across eukaryotic organisms and this process has been studied in most detail in the yeast Saccharomyces cerevisiae. Yeast ribosomes are composed of four ribosomal RNAs (rRNAs) and 79 ribosomal proteins (r-proteins). Most r-proteins need to be transported from the cytoplasm to the nucleus where they get incorporated into the evolving pre-ribosomal particles. Due to the high abundance and difficult physicochemical properties of r-proteins, their correct folding and fail-safe targeting to the assembly site depends largely on general, as well as highly specialized, chaperone and transport systems. Many r-proteins contain universally conserved or eukaryote-specific internal loops and/or terminal extensions, which were shown to mediate their nuclear targeting and association with dedicated chaperones in a growing number of cases. The 60S r-protein Rpl4 is particularly interesting since it harbours a conserved long internal loop and a prominent C-terminal eukaryote-specific extension. Here we show that both the long internal loop and the C-terminal eukaryote-specific extension are strictly required for the functionality of Rpl4. While Rpl4 contains at least five distinct nuclear localization signals (NLS), the C-terminal part of the long internal loop associates with a specific binding partner, termed Acl4. Absence of Acl4 confers a severe slow-growth phenotype and a deficiency in the production of 60S subunits. Genetic and biochemical evidence indicates that Acl4 can be considered as a dedicated chaperone of Rpl4. Notably, Acl4 localizes to both the cytoplasm and nucleus and it has the capacity to capture nascent Rpl4 in a co-translational manner. Taken together, our findings indicate that the dedicated chaperone Acl4 accompanies Rpl4 from the cytoplasm to its pre-60S assembly site in the nucleus.

SUBMITTER: Pillet B

PROVIDER: S-EPMC4598080 | biostudies-literature | 2015 Oct

REPOSITORIES: biostudies-literature

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The Dedicated Chaperone Acl4 Escorts Ribosomal Protein Rpl4 to Its Nuclear Pre-60S Assembly Site.

Pillet Benjamin B García-Gómez Juan J JJ Pausch Patrick P Falquet Laurent L Bange Gert G de la Cruz Jesús J Kressler Dieter D

PLoS genetics 20151008 10

Ribosomes are the highly complex macromolecular assemblies dedicated to the synthesis of all cellular proteins from mRNA templates. The main principles underlying the making of ribosomes are conserved across eukaryotic organisms and this process has been studied in most detail in the yeast Saccharomyces cerevisiae. Yeast ribosomes are composed of four ribosomal RNAs (rRNAs) and 79 ribosomal proteins (r-proteins). Most r-proteins need to be transported from the cytoplasm to the nucleus where they ...[more]

PMID: 26447800

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Project description:Ribosome biogenesis is a highly complex process in eukaryotes, involving temporally and spatially regulated ribosomal protein (r-protein) binding and rRNA remodeling events in the nucleolus, nucleoplasm and cytoplasm. Hundreds of assembly factors (AFs), organized into sequential functional groups, facilitate and guide the maturation process into productive assembly branches in and across different cellular compartments. However, the precise mechanisms by which these AFs function are largely unknown. Here, we use cryo-electron microscopy (cryo-EM), to characterize the structures of yeast nucleoplasmic pre-60S particles affinity-purified using the epitope-tagged AF Nog2. Our data pinpoint the locations and determine the structures of over 20 AFs, which are enriched in two areas, an arc region extending from the central protuberance (CP) to the polypeptide tunnel exit (PTE), and the domain including the internal transcribed spacer 2 (ITS2) that separates 5.8S and 25S rRNAs. These structural data suggest that the arc-located factors might function to chaperone formation of RNA helices found in the active sites of the subunit, including helices from the CP, peptidyl-transferase center (PTC) and intersubunit bridge. In particular, two regulatory GTPases, Nog2 and Nog1, act as hub proteins to interact with multiple, distant AFs and functional rRNA elements, manifesting their critical roles in structural remodeling checkpoints and nuclear export. Moreover, our snapshots of compositionally and structurally different pre-60S intermediates provide essential mechanistic details for three major remodeling events before nuclear export: rotation of the 5S RNP, construction of the active center, and ITS2 removal. Therefore, our structures provide a framework to understand the molecular roles of diverse AFs, and potentially the atomic information therein constitutes a resource to generalize principles governing the elusive functions of nuclear RNA-binding proteins.

Dataset Information

The Dedicated Chaperone Acl4 Escorts Ribosomal Protein Rpl4 to Its Nuclear Pre-60S Assembly Site.

Publications

The Dedicated Chaperone Acl4 Escorts Ribosomal Protein Rpl4 to Its Nuclear Pre-60S Assembly Site.

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