| Summary: | To further investigate the role played byRrp6p in RNA metabolism, my work aimed at identifying and characterising potential Rrp6p-associated complexes. Density gradient analyses revealed no pool of free Rrp6p, but the majority of Rrp6p was apparently associated with complexes other than exosome. In addition to the exosome, Rrp6p appeared to be associated with a 10S complex and two RNase A sensitive complexes that may correspond to pre-40S and pre-60S ribosomes. Proteomic analyses identified Gbp2p and Srp1p as potential components of the 10S complex. However, genetic analyses did not reveal defects in stable RNA synthesis in <i>gbp2 </i>or <i>srp1</i> mutant strains. Microarray analysis identified a small number of mRNAs that were upregulated in the <i>gbp2</i><i>D</i> strain. Purification of exosome complexes identified the nuclear protein Rrp47p as a substoichiometric component. Rrp47p was shown to be required for most Rrp6p functions in stable RNA synthesis but not for Rrp6p function in RNA surveillance. To better understand this similarity, I analysed the Rrp47p-exosome and the Rrp47p-Rrp6p interactions. Around 10% of the exosome was found to be associated with both Rrp6p and Rrp47p. However Rrp47p did not appear to be part of the 10S Rrp6p complex, suggesting that the surveillance functions of Rrp6p may be performed in this complex. These results have provided new insights into the function of Rrp6p in nuclear pre-mRNA turnover and into its potential association with complexes other than exosome.
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