期刊
RNA
卷 22, 期 6, 页码 852-866出版社
COLD SPRING HARBOR LAB PRESS, PUBLICATIONS DEPT
DOI: 10.1261/rna.055780.115
关键词
yeast ribosome assembly; cotranscriptional assembly; pre-rRNA processing; pre-ribosomes; hierarchical assembly
资金
- National Institutes of Health [GM28301, 1R01GM077628]
- David Scaife Family Charitable Foundation [141RA01]
- Richard King Mellon Foundation Presidential Graduate Fellowship in the Life Sciences
- Semon H. Stupakoff Scholarship
- Roche/ARCS Foundation Scholar Award
In higher eukaryotes, pre-rRNA processing occurs almost exclusively post-transcriptionally. This is not the case in rapidly dividing yeast, as the majority of nascent pre-rRNAs are processed cotranscriptionally, with cleavage at the A(2) site first releasing a pre-40S ribosomal subunit followed by release of a pre-60S ribosomal subunit upon transcription termination. Ribosome assembly is driven in part by hierarchical association of assembly factors and r-proteins. Groups of proteins are thought to associate with pre-ribosomes cotranscriptionally during early assembly steps, whereas others associate later, after transcription is completed. Here we describe a previously uncharacterized phenotype observed upon disruption of ribosome assembly, in which normally late-binding proteins associate earlier, with pre-ribosomes containing 35S pre-rRNA. As previously observed by many other groups, we show that disruption of 60S subunit biogenesis results in increased amounts of 35S pre-rRNA, suggesting that a greater fraction of pre-rRNAs are processed post-transcriptionally. Surprisingly, we found that early pre-ribosomes containing 35S pre-rRNA also contain proteins previously thought to only associate with pre-ribosomes after early pre-rRNA processing steps have separated maturation of the two subunits. We believe the shift to post-transcriptional processing is ultimately due to decreased cellular division upon disruption of ribosome assembly. When cells are grown under stress or to high density, a greater fraction of pre-rRNAs are processed post-transcriptionally and follow an alternative processing pathway. Together, these results affirm the principle that ribosome assembly occurs through different, parallel assembly pathways and suggest that there is a kinetic foot-race between the formation of protein binding sites and pre-rRNA processing events.
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