Tsr4 Is a Cytoplasmic Chaperone for the Ribosomal Protein Rps2 in Saccharomyces cerevisiae

Abstract

Eukaryotic ribosome biogenesis requires the action of approximately 200 trans-acting factors and the incorporation of 79 ribosomal proteins (RPs). The delivery of RPs to preribosomes is a major challenge for the cell because RPs are often highly basic and contain intrinsically disordered regions prone to nonspecific interactions and aggregation. To counteract this, eukaryotes developed dedicated chaperones for certain RPs that promote their solubility and expression, often by binding eukaryote-specific extensions of the RPs. Rps2 (uS5) is a universally conserved RP that assembles into nuclear pre-40S subunits. However, a chaperone for Rps2 had not been identified. Our laboratory previously characterized Tsr4 as a 40S biogenesis factor of unknown function. Here, we report that Tsr4 cotranslationally associates with Rps2. Rps2 harbors a eukaryote-specific N-terminal extension that is critical for its interaction with Tsr4. Moreover, Tsr4 perturbation resulted in decreased Rps2 levels and phenocopied Rps2 depletion. Despite Rps2 joining nuclear pre-40S particles, Tsr4 appears to be restricted to the cytoplasm. Thus, we conclude that Tsr4 is a cytoplasmic chaperone dedicated to Rps2.

yRACK1/Asc1 proxiOMICs—Towards Illuminating Ships Passing in the Night

“…The identification of known neighbors of Rps2 at ribosomes, such as Rps17, Stm1, and the translation initiation factor 3 subunits a/Rpg1 and g/Tif35 [15,46,47], proves that the Rps2-BioID method is a reliable approach to uncover proximities. Furthermore, the protein Tsr4 was just recently described as a chaperone for Rps2 and interacts with its eukaryotic-specific N-terminal region [48,49]. In total, 9 of the 16 identified Rps2-neighbors were also captured with Asc1-BirA* [18], showing that we were able to monitor a common microenvironment of both proteins at the hr40S (Figure 2B).…”

Puf6 and Loc1 Are the Dedicated Chaperones of Ribosomal Protein Rpl43 in Saccharomyces cerevisiae

“…Ribosomal proteins are very unstable because of their unique structural characteristics, which include highly positive charges and unstructured extensions. Many dedicated chaperones have been identified to protect the stability of ribosomal proteins, such as Sqt1 with Rpl10 [16,17], Acl4 with Rpl4 [18,19], Yar1 with Rps3 [20,21], Rrb1 with Rpl3 [22,23], Tsr2 with Rps26 [24,25], Syo1 with Rpl5 and Rpl11 [26,27,28], Bcp1 with Rpl23 [29], Nap1 with Rps6 [30], and Tsr4 with Rps2 [30,31] These chaperones may associate with nascent ribosomal proteins co-translationally and accompany the transport process to the assembly point [32]. They may also have additional functions in regulation.…”

“…Cells can even evolve a specialized chaperone system to interact with ribosomal proteins specifically. These dedicated chaperones could regulate the stability, transport, stoichiometry, and orientation of ribosomal proteins during the assembly process [14,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33].…”

PDCD2 functions as an evolutionarily conserved chaperone dedicated for the 40S ribosomal protein uS5 (RPS2)

“…To date, most of the evidence supporting the existence of specific ribosomal protein chaperones has been reported in the budding yeast, Saccharomyces cerevisiae . In this species, specific binding partners to a handful of ribosomal proteins have been identified and shown to be important for the accumulation of free ribosomal proteins, the import of ribosomal proteins into the nucleus, and accompanying ribosomal proteins to assembly sites in the nucleolus ( 5–10 ). Accordingly, mutations in dedicated ribosomal protein chaperones usually result in ribosome biogenesis defects that resemble those observed upon depletion of their ribosomal protein partners.…”

“…Human uS5 also forms mutually exclusive complexes with the programmed cell death 2 (PDCD2) and PDCD2-like (PDCD2L) proteins ( 15 ). Interestingly, PDCD2 and PDCD2L show homology to S. cerevisiae Tsr4, an essential protein that was recently reported to function as a dedicated chaperone for uS5 in budding yeast ( 5 , 9 ). However, in contrast to S. cerevisiae Tsr4, PDCD2L is not essential in human cells and its absence does not result in obvious defects in pre-40S maturation ( 15 ), arguing against a role for PDCD2L in chaperoning uS5 in human cells.…”