Project description:Puf6 contributes to biogenesis of the large subunit in yeast. UV-crosslinking (CRAC) was used to determine binding sites of Puf6 on RNA.
Project description:The AAA-ATPase Drg1 is a key factor in eukaryotic ribosome biogenesis that initiates cytoplasmic maturation of the large ribosomal subunit. Drg1 releases the shuttling maturation factor Rlp24 from pre-60S particles shortly after nuclear export, a strict requirement for downstream maturation. The molecular mechanism of release remained elusive. Here, we report a series of cryo-EM structures showing a hand-over-hand translocation mechanism of Drg1 and additional XL-MS data on positioning of Drg1 on pre-60S particles.
Project description:Hcr1/eIF3j is a sub-stoichiometric subunit of eukaryotic initiation factor 3 (eIF3) that can dissociate the post-termination 40S ribosomal subunit from mRNA in vitro. We examined this ribosome recycling role in vivo by ribosome profiling and reporter assays and found that loss of Hcr1 led to reinitiation of translation in 3’UTRs, consistent with a defect in recycling. However, the defect appeared to be in recycling of the 60S subunit, rather than the 40S subunit, because reinitiation did not require an AUG codon and was suppressed by overexpression of the 60S dissociation factor Rli1/ABCE1. Consistent with a 60S recycling role, overexpression of Hcr1 could not compensate for loss of 40S recycling factors Tma64/eIF2D and Tma20/MCT-1. Intriguingly, loss of Hcr1 triggered higher expression of RLI1 via an apparent feedback loop. These findings suggest Hcr1/eIF3j is recruited to ribosomes at stop codons and may coordinate the transition to a new round of translation.
Project description:In this study, we systematically identified RNAs associated with ribosomes. To identify ribosome associated RNAs, C-terminal ZZ-tagged Rpl16a or Rpl16b, expressed under control of thier native promoter, were affinity purified from whole cell extracts of cultures grown to mid-log phase in minimal medium. Extracts were incubated with immunoglobulin G (IgG) coupled microbeads, washed, and ribosomes were eluted by tobacco etch virus (TEV) protease treatment. We performed two biological replicates with each protein and analyzed the RNA content using oligo microarrays. Total RNA isolated from extracts of cells expressing Rpl16a-ZZ or Rpl16b-ZZ (input) and from the affinity-purified ribosomes was reverse transcribed with oligo(dT) primers. cDNA was labeled with Cy3 and Cy5 fluorescent dyes, respectively, and competitively hybridized to yeast oligo microarrays. Alternatively, RNA was isolated from sucrose gradient fractions containing 60S subunits, 80S monosomes and polysomes. Here, we performed four biological replicates. Analysis was done with oligo microarrays as described above. A strain or line experiment design type assays differences between multiple strains, cultivars, serovars, isolates, lines from organisms of a single species. strain_or_line_design
Project description:Many unannotated microproteins and alternative proteins (alt-proteins) have recently been found to be co-encoded with canonical proteins, but few of their functions are known. Motivated by the hypothesis that alt-proteins undergoing regulated synthesis could play important cellular roles, we developed a chemoproteomic pipeline to identify nascent alt-proteins in human cells. We identified 22 actively translated alt-proteins or N-terminal extensions, one of which is post-transcriptionally upregulated by DNA damage stress. We further defined cell cycle-regulated MINAS-60 (MIcroprotein that Negatively regulates ASsembly of the pre-60S ribosomal subunit), a nucleolar alt-protein co-encoded with human RBM10. Depletion of MINAS-60 increases the amount of cytoplasmic 60S ribosomal subunit, upregulating global protein synthesis and cell proliferation. Mechanistically, MINAS-60 represses the rate of late-stage pre-60S assembly and export to the cytoplasm. Together, these results implicate MINAS-60 as a repressor of pre-60S maturation, and demonstrate that chemoproteomics can enable functional hypothesis generation for uncharacterized alt-proteins.
Project description:The REIL proteins are required for late ribosomal biogenesis and accumulation of the 60S large ribosome subunit in mature leaves of Arabidopsis thaliana upon acclimation to low temperature. To validate these functions in roots, we conducted a multi-level system analysis targeted at understanding defects and compensations responses of reil mutants before acclimation to low temperature and following temperature shift. Hydroponic root tissue enabled analysis of eukaryotic ribosome complexes with negligible interference of organelle ribosomes. Hydroponic cultivation attenuated the growth defect of reil mutants at low temperature and provided new insights into the primary functions of Arabidopsis REIL proteins. Arabidopsis tightly controls the balance of non-translating 40S and 60S subunits. Reil mutants initially deplete both non-translating subunits upon shift to 10°C and subsequently replenish these pools slowly. Reil mutations compensate the 60S biosynthesis defect by increased baseline levels of non-translating 40S and 60S subunits and depletion of a likely non-translating, KCl-sensitive 80S sub-fraction in the cold. We infer that Arabidopsis buffers fluctuating translation demands following temperature cues by activating non-translating ribosome fractions before de novo synthesis meets temperature-induced demands. Reil1 reil2 double mutants accumulate 43S-preinitiation complexes and pre-60S-maturation complexes and affect the paralog composition of non-translating ribosome fractions. With few exceptions, e.g. RPL3B and RPL24C, these changes were not under transcriptional control. Our study suggests requirement of de novo synthesis of eukaryotic ribosomes for long-term cold acclimation. Double mutant analysis indicates feedback control of REIL-mediated 60S maturation on NUC2 and eIF3C2 transcription and implies functions of two so far non-described proteins in late plant ribosome biogenesis. We propose that Arabidopsis requires biosynthesis of specialized ribosomes for successful cold acclimation.