Caenorhabditis elegans operons: form and function

Key Points C. elegans is unusual among animals in having operons. These contain co-transcribed genes that make a polycistronic pre-mRNA that is subsequently separated into single-gene mRNAs by 3′-end formation and trans -splicing. Approximately 15% of C. elegans genes are encoded in operons that contain 2–8 genes. Operon-like multigene assemblies are also found in other nematodes and in other species that process their pre-mRNAs using spliced-leader-type trans -splicing. Operons sometimes co-regulate genes that make proteins with related functions. The study of genes that are co-transcribed in C. elegans operons might be a useful tool to identify the proteins that are functionally related to a particular gene of interest. Some functional classes of gene are preferentially included in operons, whereas others are excluded or rarely included. Genes that encode the proteins that function in RNA degradation are the class most frequently included in operons. Other frequently included groups include all of the genes that encode the basic machinery of transcription, RNA splicing and translation, as well as those that encode mitochondrial proteins. We speculate that operons facilitate global regulation of the basic gene expression and energy generation machinery of the cell, in response to signals that are unknown at present. Nematodes are unusual among animals in having a substantial proportion of their genes arranged in polycistronic clusters that are similar to bacterial operons. Recently, a nearly complete database of the Caenorhabditis elegans genes that are transcribed in operons has been produced. Analysis of this database has identified the types of genes that are contained in the operons and the extent to which operons co-regulate genes of related function.