Tsr4 and Nap1, two novel members of the ribosomal protein chaperOME

Abstract

Dedicated chaperones protect newly synthesized ribosomal proteins (r-proteins) from aggregation and accompany them on their way to assembly into nascent ribosomes. Currently, only nine of the ∼80 eukaryotic r-proteins are known to be guarded by such chaperones. In search of new dedicated r-protein chaperones, we performed a tandem-affinity purification based screen and looked for factors co-enriched with individual small subunit r-proteins. We report the identification of Nap1 and Tsr4 as direct binding partners of Rps6 and Rps2, respectively. Both factors promote the solubility of their r-protein clients in vitro. While Tsr4 is specific for Rps2, Nap1 has several interaction partners including Rps6 and two other r-proteins. Tsr4 binds co-translationally to the essential, eukaryote-specific N-terminal extension of Rps2, whereas Nap1 interacts with a large, mostly eukaryote-specific binding surface of Rps6. Mutation of the essential Tsr4 and deletion of the non-essential Nap1 both enhance the 40S synthesis defects of the corresponding r-protein mutants. Our findings highlight that the acquisition of eukaryote-specific domains in r-proteins was accompanied by the co-evolution of proteins specialized to protect these domains and emphasize the critical role of r-protein chaperones for the synthesis of eukaryotic ribosomes.

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

“…However, truncations from either end of the protein resulted in a loss of interaction and were uninformative (data not shown). Similar results were recently reported by a study that was published while this article was in review (35). Considering that the related YwqG protein folds into a single globular domain (30), Tsr4 does not seem amenable to domain mapping via serial truncations.…”

“…Here, we provide evidence that these eukaryotic extensions of Rps2 drive its interaction with Tsr4, which we identify as a dedicated cytoplasmic chaperone for Rps2. A complementary study reporting that Tsr4 is a chaperone of Rps2 was published while this article was in review (35). Like other chaperones of RPs, Tsr4 finds its client protein cotranslationally, recognizing the N-terminal extension of Rps2 as it emerges from the ribosome.…”

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].…”