The frataxin-encoding operon of Caenorhabditis elegans shows complex structure and regulation

The genome of the nematode Caenorhabditis elegans is unusual among eukaryotes, in that it contains operons. Approximately 15% of genes in the worm are clustered into groups of between two and eight genes, which are under the control of shared regulatory sequences. Polycistronic transcripts from such operons are trans-spliced, during transcription, to produce mature monocistronic messengers. The C. elegans frataxin gene, frh-1, is encoded in the operon CEOP2232. This is one of the largest operons identified thus far in the C. elegans genome. Here we describe in detail the structure of all of the coding units within this operon. The operon is composed of eight genes of a diverse nature, organized in a complex structure. We have produced transgenic strains carrying fusions between gfp and a number of genes from the operon. These constructs show complex differential expression patterns that suggest the presence of internal promoters and regulatory sequences in the operon. This organization would permit both coordinated expression and differential expression of the components of the CEOP2232 operon. The heterogeneity of the genes, and their complex expression patterns, suggests that the clustering of CEOP2232 is not due to a need for synchronized expression of genes involved in the same physiological pathway.