Conservation of gene co-regulation in prokaryotes and eukaryotes

Genes that are part of the same operon in prokaryotes, or have the same expression pattern in eukaryotes, are transcriptionally co-regulated. If genes are consistently co-regulated across distantly related organisms, the genes have closely associated functions. It has been shown previously that such genes have a strong tendency to belong to the same protein complex in prokaryotes, and we show by an analysis of the sequences and their expression in the yeast Saccharomyces cerevisiae and the worm Caenorhabditis elegans that this is also true for eukaryotes. Our analysis reveals that the number of conserved co-regulated genes is small in eukaryotes, as has been shown previously in prokaryotes, indicating that there are extensive variations in the gene regulatory network across organisms.