Hermes Transposon Mutagenesis of the Fission Yeast Genome

Non-protein-coding regions of eukaryotic genomes remain poorly understood. Diversity studies, comparative genomics and biochemical outputs of genomic sites can be indicators of functional elements, but none produce fine-scale genome-wide descriptions of all functional elements in a genome. As a step towards a comprehensive description of functional elements in the Schizosaccharomyces pombe genome, we generated transposon mutagenesis libraries to a density of one insertion per 13 nucleotides of the haploid genome. We applied a five-state hidden Markov model (HMM) to characterise insertion-depleted regions at nucleotide-level resolution. HMM-defined functional constraint was consistent with genetic diversity, comparative genomics, gene-expression data and genome annotation. We infer that transposon insertions lead to fitness consequences in 90% of the genome, including 80% of the non-protein-coding regions, reflecting the presence of numerous non-coding elements in this compact genome that have functional roles. Display of this data in genome browsers provides fine-scale views of structure-function relationships within specific genes.