Determining the region of Rpl10 crucial for Nmd3 release in the 60S subunit pathway of ribosomal biogenesis
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The large ribosomal subunit of the ribosome is exported out of the nucleus with the help of a protein known as Nmd3. Nmd3 interacts with the large ribosomal subunit and provides a nuclear export signal, which recruits export receptors and thereby facilitates subunit export from the nucleus. However, in order for more large ribosomal subunits to be able to be exported from the nucleus, Nmd3 must be released from the ribosome in the cytoplasm and recycled back to the nucleus. Rpl10 is a protein of the large ribosomal subunit that is required for the release of Nmd3 from the large ribosomal subunit and allows it to be recycled back to the nucleus, though the exact mechanism of Nmd3 release is unknown. A mutant NMD3 I112T I362T allele has been shown to suppress a mutant rpl10 G161D allele, thus suggesting some type of interaction between the Nmd3 and Rpl10 proteins. Further studies have shown that Nmd3 and Rpl10 do not physically interact with each other; however, Rpl10 has been shown to interact with tRNA and rRNA, thus possibly providing a means by which Rpl10 may indirectly affect Nmd3 release. A genetic screen was devised to identify mutations in RPL10 that are dependent on NMD3 I112T I362T for survival. These mutations in RPL10 were mapped onto the atomic structure of Rpl10 in the ribosome. While the mutations did not map to any one location on Rpl10, two clusters of three mutations each were identified, one near the N-terminus of the protein and another near the C-terminus of the protein, both containing residues that could interact with rRNA nearby, as well as residues that could interact with other residues internal to Rpl10 and thus affect the overall structure of the protein. Thus, it may be possible that Rpl10 affects Nmd3 release indirectly through accommodation of Rpl10 onto the ribosome via protein-rRNA interactions that affect Nmd3-rRNA interactions.