A Molecular Portrait Of De Novo Genes

Abstract

New genes, with novel protein functions, can evolve \"from scratch\" out of intergenic sequences. These de novo genes can integrate the cells genetic network and drive important phenotypic innovations. Therefore, identifying de novo genes and understanding how the transition from noncoding to coding occurs are key problems in evolutionary biology. However, identifying de novo genes is a difficult task, hampered by the presence of remote homologs, fast evolving sequences and erroneously annotated protein coding genes. To overcome these limitations, we developed a procedure that handles the usual pitfalls in de novo gene identification and predicted the emergence of 703 de novo genes in 15 yeast species from two genera whose phylogeny spans at least 100 million years of evolution. We established that de novo gene origination is a widespread phenomenon in yeasts, only a few being ultimately maintained by selection. We validated 82 candidates, by providing new translation evidence for 25 of them through mass spectrometry experiments. We also unambiguously identified the mutations that enabled the transition from non-coding to coding for 30 Saccharomyces de novo genes. We found that de novo genes preferentially emerge next to divergent promoters in GC-rich intergenic regions where the probability of finding a fortuitous and transcribed ORF is the highest. We found a more than 3-fold enrichment of de novo genes at recombination hot spots, which are GC-rich and nucleosome-free regions, suggesting that meiotic recombination would be a major driving force of de novo gene emergence in yeasts.