[FI2020] Molecular Mechanisms of pre-mRNA Splicing

Most eukaryotic transcripts carry information split in exons interrupted by introns. The process of precise intron removal and exon joining, known as pre-mRNA splicing, is catalyzed by the spliceosome, arguably the cell’s most complex molecular machine. The chemistry of splicing is simple: two consecutive transesterifications (“steps” in splicing). Why then a machine larger than a full ribosome? As an error of a single nucleotide could change the entire mRNA, it is reasonable to expect that most of the spliceosome’s intricacies are devoted to proper substrate recognition during both steps. This becomes more evident when alternative splicing is considered. By adding flexibility to intron and exon recognition, alternative splicing expands the genetic information content of genomes and provides an additional layer of control to gene expression. Each eukaryotic gene actually produces a fine-tuned collection of diverse transcripts in precise proportions. Perturbations in this balance can have a profound impact on both the cell’s viability and the health of the organism.

Accordingly, understanding the ways of the spliceosome is a pressing endeavor, notwithstanding the great advances in the field. It soon became clear that the fundamentals of this enzyme are highly conserved in evolution, and this notion has been further validated by spectacular advances in determining its molecular structure at atomic resolution.  Motivated by this, we put forward a reductionist approach to study the spliceosome basic features that support alternative splicing. Our working hypothesis is that the molecular actuators of the spliceosome that are the root of its control can be better identified in a system where they act unmasked by other splicing factors. Yeast is one of these systems as opposed to more complex organisms, such as human, where both the number of additional factors that control splicing is in the hundreds, and the ways of experimental manipulation are not that many. Yeast cells, on the other hand, can be easily manipulated and go by with the core spliceosome and a handful of regulatory factors. Yet, the yeast spliceosome can be regulated, senses chromatin status, and is capable of such sophisticated schemes as exon definition. Indeed, our preliminary data indicate that exonic mutations that change exon definition in humans have an analogous phenotype in yeast cells. Encouraged by these findings we would like to develop a PhD Thesis project and therefore seek a candidate for a FI fellowship from the Catalan Government (http://agaur.gencat.cat/en/beques-i-ajuts/convocatories-per-temes/Ajuts…). Given the requirements and number of FI fellowships, only students with the highest grades can be considered. If successful, the student will undertake a research project focused on the molecular properties of the core spliceosome (using the yeast one as a proxy) that participate, either at it