Talk: Transcriptional activity is the default state of eukaryotic DNA

Overview:Genomes encode for genes and the gene regulatory signals that enable those genes to be transcribed, and are continually shaped through evolution. Genomes, including that of human and yeast, encode for numerous transcripts that have limited evidence of conservation or function. Most protein coding transcripts and some non-coding transcripts are thought to be functionally important, but many non-coding transcripts may represent noise in the transcriptional machinery. Here, we sought to create a transcriptional null hypothesis by quantifying the transcriptional activity of evolutionarily naïve DNA, using human DNA expressed in yeast and computational predictions of random DNA activity in human. In yeast, we found that transcription is the default DNA state, with most bases expressed as part of one or more heterogeneous transcripts, suggesting that selection has shaped the yeast genome into coherent gene structures. Our results indicate that achieving the transcriptional signals needed for de novo gene birth is comparatively easy, and is unlikely to be a rate limiting step in de novo gene evolution. Further, this suggests that, rather than non-coding transcripts evolving from non-transcribed regions, they are expected to occur by chance, where they have the potential to evolve a function or, if sufficiently detrimental, selection may act to repress them.