The existence of introns in genome is a real mystery, given the expensive energy cost for a cell to pay for copying the entire length of several introns in a gene and excising them at the exact position, controlled by big RNA and protein complexes after transcription. Nevertheless, most completely genomes of eukaryotic cells so far carry introns in their genomes [6970], and some studies even showed that introns had been propagated during eukaryotic lineage evolution [39717273]. The origin of spliceosomal introns in eukaryotic lineage has been attempted to be explained by the massive invasion of group II self-splicing introns from bacteria to eukaryotes [35]. It is very hard to understand how and why introns propagate in eukaryotic lineages and what the beneficial effect of introns on cell survival is.
