Eukaryotic 60S ribosomal subunits are comprised of three rRNAs and ∼50 ribosomal proteins. The initial steps of their formation take place in the nucleolus, but, owing to a lack of structural information, this process is poorly understood. Using cryo-EM, we solved structures of early 60S biogenesis intermediates at 3.3 Å to 4.5 Å resolution, thereby providing insights into their sequential fold...

The cauliflower mosaic virus transactivator, TAV, controls translation reinitiation of major open reading frames on polycistronic RNA. We show here that TAV function depends on its association with polysomes and eukaryotic initiation factor eIF3 in vitro and in vivo. TAV physically interacts with eIF3 and the 60S ribosomal subunit. Two proteins mediating these interactions were identified: eIF3...

Ribosomal proteins play important roles in ribosome biogenesis and function. Here, we study the evolutionarily conserved L26 in Saccharomyces cerevisiae, which assembles into pre-60S ribosomal particles in the nucle(ol)us. Yeast L26 is one of the many ribosomal proteins encoded by two functional genes. We have disrupted both genes; surprisingly, the growth of the resulting rpl26 null mutant is ...

The Saccharomyces cerevisiae ribosomal protein rp51 is encoded by two interchangeable genes, RP51A and RP51B. We altered the RP51 gene dose by creating deletions of the RP51A or RP51B genes or both. Deletions of both genes led to spore inviability, indicating that rp51 is an essential ribosomal protein. From single deletion studies in haploid cells, we concluded that there was no intergenic dos...

Several mutants ( spb1 - spb7 ) have been previously identified as cold-sensitive extragenic suppressors of loss-of-function mutations in the poly(A)(+)-binding protein 1 of Saccharomyces cerevisiae. Cloning, sequence and disruption analyses revealed that SPB1 (YCL054W) encodes an essential putative S -adenosylmethionine-dependent methyltransferase. Polysome analyses showed an under-accumulatio...

The interleukin enhancer binding factors ILF2 (NF45) and ILF3 (NF90/NF110) have been implicated in various cellular pathways, such as transcription, microRNA (miRNA) processing, DNA repair, and translation, in mammalian cells. Using tandem affinity purification, we identified human NF45 and NF90 as components of precursors to 60S (pre-60S) ribosomal subunits. NF45 and NF90 are enriched in nucle...

Kap123p is a yeast beta-karyopherin that imports ribosomal proteins into the nucleus prior to their assembly into preribosomal particles. Surprisingly, Kap123p is not essential for growth, under normal conditions. To further explore the role of Kap123p in nucleocytoplasmic transport and ribosome biogenesis, we performed a synthetic fitness screen designed to identify genes that interact with KA...

We report the characterization of the yeast Npa2p (Urb2p) protein, which is essential for 60S ribosomal subunit biogenesis. We identified this protein in a synthetic lethal screening with the rsa3 null allele. Rsa3p is a genetic partner of the putative RNA helicase Dbp6p. Mutation or depletion of Npa2p leads to a net deficit in 60S subunits and a decrease in the levels all 27S pre-rRNAs and mat...

The yeast nucleolar protein Nop8p has previously been shown to interact with Nip7p and to be required for 60S ribosomal subunit formation. Although depletion of Nop8p in yeast cells leads to premature degradation of rRNAs, the biochemical mechanism responsible for this phenotype is still not known. In this work, we show that the Nop8p amino-terminal region mediates interaction with the 5.8S rRN...

The biogenesis of ribosomes is coordinated with cell growth and proliferation. Distortion of the coordinated synthesis of ribosomal components affects not only ribosome formation, but also cell fate. However, the connection between ribosome biogenesis and cell fate is not well understood. To establish a model system for inquiries into these processes, we systematically analyzed cell cycle progr...