The synthesis of ribosomes is a major metabolic pathway in all cells. In eukaryotes, a polycistronic pre-ribosomal RNA transcript is processed to the mature 18S, 5.8S and 25S/28S rRNAs, whilst undergoing extensive covalent nucleotide modifications and assembling with the ~80 ribosomal proteins. More than 140 known factors are required for post-transcriptional steps in ribosome synthesis in yeast and, although the processing of ribosomal RNA precursors is fairly well understood, the relationship between ribosomal processing, ribosome assembly, subunit export and subnucleolar structures is still largely unclear. To gain insights into these processes, I analysed three previously uncharacterised ribosomal factors. To study their involvement in the ribosomal RNA processing and assembly, conditional alleles were generated of the essential genes <i>NOP7, RRP12 </i>and <i>NOP15</i>, as well as epitope-tagged versions of their protein products. The nucleolar protein Nop7p has multiple roles in the synthesis of the 60S ribosomal subunit and is required for efficient 5’ to 3’ exonuclease digestion that generates the 5’ end of the major, short form of the 5.8S rRNA, assembly and export of the 60S ribosomal subunit. Nop15p is also needed for normal 5’ to 3’ exonuclease digestion and, additionally, for processing of residual 27SB to 7S pre-rRNA. Nop15p Contains an RNA recognition domain and is therefore likely to associate directly with the pre-rRNA to facilitate its processing. Rrp12p is the only <i>trans</i>-acting factor known to be required during late maturation of both ribosomal subunits. The protein appears to fulfil very different roles in the different subunits, as assembly factor and facilitator of exosome activity in the large subunit, and during export of the small subunit. Rrp12p is predicted to be composed of HEAT-repeats and is therefore structurally related to importin β-like family of export and import receptors. Several ribosomal processing factors, including Nop7 and Nop15p, seem to be multifunctional with roles in different cellular processes suggesting that major metabolic processes within the cell may be linked.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660164 |
| Date | January 2002 |
| Creators | Oeffinger, Marlene |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/11227 |
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