CYCLOPHILIN AND PROTEIN DISULFIDE-ISOMERASE GENES ARE CO-TRANSCRIBED IN A FUNCTIONALLY RELATED MANNER IN CAENORHABDITIS-ELEGANS

The ubiquitous enzymes peptidlyl prolyl cis-trans isomerase (PPI, EC 5 .2.1.8) and protein disulfide isomerase (PDI, EC 5.3.4.1) are importan t rate-limiting catalysts of protein-folding events in the cell, In th e free-living nematode Caenorhabditis elegans, two genes encoding thes e enzymes (cyp-9 and pdi-1, respectively) are clustered together on ch romosome Ln. In work described elsewhere, the encoded enzymes have bee n expressed as recombinant proteins and have been determined to posses s in vitro PPI and PDI activity, Taken together, this organization of the two genes and the related functions of their transcripts indicate that they may be cotranscribed as a polycistronic unit, similar to bac terial operons, This study details the very close linkage of pdi-1 and cyp-9, which are in the same orientation, pdi-1 is the upstream gene, and the putative polyadenylation cleavage signal of this gene is sepa rated from the trans-splice acceptor site of cyp-9 by only 103 bp, pdi -1 is trans-spliced by the ubiquitous nematode trans-spliced leader SL 1, whereas cyp-9 was found to be predominantly trans-spliced by the '' operon-specific'' trans-spliced leader SL2. Similar trends in relative transcript abundance were demonstrated with synchronously produced mR NA for both genes during larval development, supporting the contention that the genes are co-expressed, Finally, reporter gene analysis prov ides strong evidence that both genes are controlled by a single upstre am regulatory element, which directs expression of both enzymes in the hypodermal cells that synthesize the cuticle.