Itoh T, Takemoto K, Mori H, Gojobori T.

Mol Biol Evol. 1999 Mar;16(3):332-46. doi:10.1093/oxfordjournals.molbev.a026114

Evolutionary instability of operon structures disclosed by sequence comparisons of complete microbial genomes.

Search accross prokaryotes, archea and eukaryotes. No operon conservation between bacteria and yeast, except perhaps gal. Many operons destroyed in bacteria, although some very conserved ones remain (for instance for ribosomal proteins). Proposes a partimonious way to estimate operon creation and destruction.