A recent report by Blumenthal et al. provides convincing evidence that at least 
15% of Caenorhabditis elegans genes are co-transcribed within over a thousand 
operons. Polycistronic transcription of gene clusters is very rare in 
eukaryotes. The widespread occurrence of operons in C. elegans thus raises some 
interesting questions about the origin and function of these multigenic 
transcriptional units.