Abstract #58

Splicing is rapidly and specifically regulated in response to environmental changes. Gregg Whitworth, Jeffrey A Pleiss, Megan Bergkessel, Christine Guthrie. Biochemistry & Biophysics, UCSF, San Francisco CA.
   In higher eukaryotes, where most genes are interrupted by multiple introns, it is clear that both the timing and diversity of protein expression can be regulated at the level of pre-mRNA splicing. The yeast Saccharomyces cerevisiae lacks many of the hallmarks of alternative splicing: less than 5% of genes contain an intron, most genes contain a single intron, sequences generally adhere to a strict consensus at the splice sites, and there are few if any SR proteins that affect splicing. Nonetheless, the spliceosome itself is highly conserved between yeast and metazoans. Moreover, the set of intron-containing genes in yeast includes factors involved in setting the physiological state of the cell, such as components of the translational, cytoskeletal and secretory machineries, raising the possibility that splicing has been maintained in yeast to regulate gene expression. To address this question, we have used a microarray-based strategy to examine the kinetic response of splicing to a wide range of environmental conditions. Within minutes after the addition of 3-AT, a drug used to induce amino acid starvation, the splicing of the majority of intron-containing ribosomal protein transcripts is inhibited, while all other spliced transcripts are unaffected. Remarkably, deletion of GCN2, the non-essential kinase which modulates both the transcriptional and translational responses to amino acid starvation, has no effect on the splicing phenotype. Likewise, deletion of TOR1, a kinase responsible for ribosomal regulation under a variety of conditions, has no effect on the phenotype. Together, these results suggest that a novel sensing pathway is responsible for communicating the starvation state to the spliceosome. By comparison, osmotic stress has no effect on the splicing of the ribosomal protein genes but does rapidly down-regulate the splicing of a small and non-overlapping set of transcripts. These rapid, combinatorial, transcript-specific responses suggest that splicing can provide an important mechanism for global regulation of gene expression at the post-transcriptional level.

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