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.