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In Saccharomyces cerevisiae, nuclear events of gene expression, especially those involved in pre-mRNA capping, splicing, cleavage and polyadenylation do not function with absolute precision. The inaccuracy associated with these processing events results in the formation of aberrant messenger RNAs. Interestingly, these abnormal messages, undergo a very efficient nuclear surveillance mechanism via a rapid degradation by two nuclear pathways of mRNA decay, namely (a) DRN dependent on Cbc1p and Rrp6p proteins (1, 2) and (b) exosome mediated nuclear mRNA decay pathway dependent on ten 3´5´ exoribonucleases and four associated factors including Rrp6p, (3,4). Besides the aberrant mRNAs Exosome/DRN mechanisms also known to degrade a small subset of normal mRNAs which were termed as special mRNAs. It was proposed that the normal physiological level of these mRNAs in the cell is maintained by DRN/Exosome. Two examples of such post-transcriptional regulation of Gene expression will be presented. |