Brian Sajorda BA, Jana Bregman MD, Jonathan Taylormoore MD, Bethany Karwoski MD, Kelly Hutcheson MD, William Madigan MD, Richard Birdsong MD, Monica Manrique MD, Heather de Beaufort MD
Cedric Lansangan & Jane C. Kim
Department of Biological Sciences, California State University - San Marcos
A key feature required for cell survival is genomic stability, which is the ability of a cell to prevent and repair mutations in its genome. Genomic mutations can be generated in several ways, including transcription of a gene via transcription-associated mutagenesis (TAM). The impact of splicing on TAM is not well understood. Here, our work investigated the effect which splicing has on the rate of TAM in a URA3 reporter gene using the budding yeast Saccharomyces cerevisiae as a model organism. Fluctuation assays were used to measure mutation rates. Our results suggest that the presence of introns in the natively-intronless URA3 gene is associated with elevated mutation rates of that gene in an intron-length-dependent manner (i.e. the yeast strains with a long intron reproducibly demonstrated elevated URA3 gene mutation rates compared to those of the strains with either a short intron or no intron). The increased transcription rate of galactose-inducible variants of these strains led to a similar effect. First exon length (i.e. intron proximity to the promoter) appears to also play a role since the distally-located long intron, but not the proximally-located long intron, displayed a similar mutation rate as our other long intron strains. Future work will assess URA3 reporter gene expression levels in each strain to support mutagenesis results. Collectively, our findings contribute to better understanding the impact of splicing on the mutagenesis of highly-expressed genes, which may play a role in spontaneous mutagenesis in the human genome.
Keywords: mutagenesis, introns, yeast