A RanGTP-independent mechanism allows ribosomal protein nuclear import for ribosome assembly

Schütz, Sabina; Fischer, Ute; Altvater, Martin; Nerurkar, Purnima; Peña, Cohue; Gerber, Michaela; Chang, Yeon Soo; Caesar, Stefanie; Schubert, Olga T.; Schlenstedt, Gabriel; Panse, Vikram Govind

doi:10.7554/elife.03473

Cited by 65 publications

(124 citation statements)

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“…(uL4), and they are imported to the nucleus together (52,53); and Tsr2 works as an escortin of Rps26 (eS26) (54). Here, we reported that Puf6 and Loc1 work together to ensure the efficient accommodation of Rpl43 into the ribosome.…”

Section: Discussionmentioning

confidence: 94%

The Roles of Puf6 and Loc1 in 60S Biogenesis Are Interdependent, and Both Are Required for Efficient Accommodation of Rpl43

Yang

Ting

Liang

et al. 2016

Journal of Biological Chemistry

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Puf6 and Loc1 have two important functional roles in the cells, asymmetric mRNA distribution and ribosome biogenesis. Puf6 and Loc1 are localized predominantly in the nucleolus. They bind ASH1 mRNA, repress its translation, and facilitate the transport to the daughter cells. Asymmetric mRNA distribution is important for cell differentiation. Besides their roles in mRNA localization, Puf6 and Loc1 have been shown to be involved in 60S biogenesis. In puf6⌬ or loc1⌬ cells, pre-rRNA processing and 60S export are impaired and 60S subunits are underaccumulated. The functional studies of Puf6 and Loc1 have been focused on ASH1 mRNA pathway, but their roles in 60S biogenesis are still not clear. In this study, we found that Puf6 and Loc1 interact directly with each other and both proteins interact with the ribosomal protein Rpl43 (L43e). Notably, the roles of Puf6 and Loc1 in 60S biogenesis are interdependent, and both are required for efficient accommodation of Rpl43. Loc1 is further required to maintain the protein level of Rpl43. Additionally, the recruitment of Rpl43 is required for the release of Puf6 and Loc1. We propose that Puf6 and Loc1 facilitate Rpl43 loading and are sequentially released from 60S after incorporation of Rpl43 into ribosomes in yeast.Almost every process in a cell is mediated by proteins, the products of translating mRNA by ribosomes. Ribosomes are composed of two subunits, a small subunit and a large subunit, 40S and 60S, respectively, in eukaryotic cells. In Saccharomyces cerevisiae, the 40S and 60S subunits are assembled from a large primary 35 S rRNA transcribed by RNA polymerase I. Processing of this rRNA yields 5.8S, 18S, and 25S rRNAs. The 5S rRNA is transcribed by RNA polymerase III separately (see reviews in Refs. 1-4). In yeast, 5S, 5.8S, and 25S (28S in higher eukaryotes) rRNA assemble with 39 ribosomal proteins to make up the 60S subunit, whereas 18S rRNA and 33 ribosomal proteins constitute the 40S subunit (5-7).Ribosome biogenesis is necessary for cell growth and proliferation. The synthesis of ribosome is a complex pathway in which over 200 trans-acting factors are involved. Many of the RNA folding, protein assembly, and maturation events are hierarchical, requiring the correct completion of one event to progress to the next event. This is seen in the assembly of ribosomal proteins onto the RNA in bacterial ribosome assembly (8) as well as in cytoplasmic maturation of the large subunit in yeast (9, 10). In addition, trans-acting factors also perform quality control steps for the assembly of the protein synthesis machinery. Syo1 facilitates the synchronized import of the two 5S rRNA-binding proteins, Rpl5 and Rpl11, to ensure stoichiometric the incorporation of these two proteins into the pre-60S subunits and also works as an assembly platform for the 5S ribonucleoprotein (RNP) (11,12). Release of the anti-association factor Tif6 requires elongation factor-like Efl1 and tRNAlike Sdo1 to confirm the integrity of the P-site (13-15). Transacting factors on cytoplasmic pre-40S subuni...

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Section: Discussionmentioning

confidence: 94%

The Roles of Puf6 and Loc1 in 60S Biogenesis Are Interdependent, and Both Are Required for Efficient Accommodation of Rpl43

Yang

Ting

Liang

et al. 2016

Journal of Biological Chemistry

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“…It has been shown that karyopherins or chaperones interact with ribosomal proteins to maintain their solubility and also facilitate their loading into nascent ribosomal subunits (33)(34)(35)(36)(37)(38)(39)(40)(41)(42).…”

Section: Figure 2 the Function Of Bcp1 Is Tightly Connected With Manmentioning

confidence: 99%

“…Recently, Tsr2 was reported as an escortin to dissociate eS26 from karyopherins in a Ran-GTP-independent manner and for proper delivery of eS26 to nascent 40S subunits (40). Because Kaps do not interact efficiently with the complex of Bcp1 and Rpl23, we tested whether Bcp1 could compete with Kaps for Rpl23.…”

Section: Figure 2 the Function Of Bcp1 Is Tightly Connected With Manmentioning

confidence: 99%

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Bcp1 Is the Nuclear Chaperone of Rpl23 in Saccharomyces cerevisiae

Ting

Johnson

et al. 2017

Journal of Biological Chemistry

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Edited by Linda SpremulliEukaryotic ribosomes are composed of rRNAs and ribosomal proteins. Ribosomal proteins are translated in the cytoplasm and imported into the nucleus for assembly with the rRNAs. It has been shown that chaperones or karyopherins responsible for import can maintain the stability of ribosomal proteins by neutralizing unfavorable positive charges and thus facilitate their transports. Among 79 ribosomal proteins in yeast, only a few are identified with specific chaperones. Besides the classic role in maintaining protein stability, chaperones have additional roles in transport, chaperoning the assembly site, and dissociation of ribosomal proteins from karyopherins. Bcp1 has been shown to be necessary for the export of Mss4, a phosphatidylinositol 4-phosphate 5-kinase, and required for ribosome biogenesis. However, its specific function in ribosome biogenesis has not been described. Here, we show that Bcp1 dissociates Rpl23 from the karyopherins and associates with Rpl23 afterward. Loss of Bcp1 causes instability of Rpl23 and deficiency of 60S subunits. In summary, Bcp1 is a novel 60S biogenesis factor via chaperoning Rpl23 in the nucleus.The ribosome is a large macromolecular complex responsible for decoding cellular genetic information into proteins. There are two ribosomal subunits; in the eukaryotes, they are the (60S) large subunit and the small (40S) subunit, each composed of both rRNAs and ribosomal proteins. In eukaryotic cells, the assembly of ribosomes occurs in the nucleolus, a subcompartment of the nucleus devoted to ribosome biogenesis. rRNAs are transcribed by RNA polymerase I and III, and the initial assembly and processing events occur co-transcriptionally. The mRNAs of ribosomal proteins are transcribed in the nucleus by RNA polymerase II and translated in the cytoplasm. Consequently, the ribosomal proteins must be imported into the nucleus for assembly with the rRNAs. After ribosome assemblies have achieved a certain stage of maturation, export factors are loaded to direct these huge complexes to cross the nuclear membrane through the nuclear pore complexes (1-6). In the cytoplasm, ribosomes undergo additional steps in the maturation process; the trans-acting factors that are exported with nascent ribosomal subunits need to be stripped off, additional ribosomal proteins are added, and in the case of the 40S subunit, the final rRNA processing occurs (7,8). The synthesis of ribosomes requires the coordination of many non-ribosomal trans-acting factors at different stages for this pathway to be completed. About 200 trans-acting factors are involved in rRNA processing, rRNA folding, protein loading, and export. To date, more trans-acting factors have continued to be identified (7, 9, 10).BCP1 is an essential gene involved in the export of Mss4 (11), a phosphatidylinositol (PI) 2 4-phosphate 5-kinase that catalyzes the phosphorylation of PI4-phosphate and acts with the PI4-kinase, Stt4p, at the plasma membrane to generate PI4,5P 2 (12, 13). Phosphoinositols are critical small signal...

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“…For many years, it was unclear how these intrinsically unstable and aggregation-prone proteins are targeted to the ribosome assembly site in the nucleolus. Work from the Panse laboratory recently identified a first carrier, termed an escortin, that fulfills this targeting role, linking the nuclear import machinery with the ribosome assembly pathway (Sch€ utz et al, 2014). Specifically, the escortin Tsr2 coordinates the transfer of the r-protein eS26 after nuclear import to the assembling 90S preribosome.…”

Section: Assembly Of 90s Preribosome Earliest Ribosomal Precursormentioning

confidence: 99%