OPERONS AS A COMMON FORM OF CHROMOSOMAL ORGANIZATION IN C-ELEGANS

ALTHOUGH eukaryotic genes are usually transcribed individually, at lea st a few Caenorhabditis elegans genes appear to be transcribed polycis tronically in clusters resembling bacterial operons(1). The spliced le ader SL2 (ref. 2) is specific for trans-splicing to downstream genes i n these operons(1). In addition, many C. elegans pre-mRNAs are trans-s pliced to SL1 (ref. 3) near the 5' ends of pre-mRNAs(4,5). Because ope rons have not previously been found in higher eukaryotes, we have inve stigated how widespread they are in the C. elegans genome. We identifi ed gene clusters using the extensive data generated by the genome proj ect(6,7) and tested seven for trans-splicing specificity. All were fou nd to fit expectations for polycistronic transcription. In addition, w e surveyed reported C. elegans genes for irans-splicing specificity. B oth methods indicate that the pre-mRNAs of about 70% of C. elegans gen es are trans-spliced and as many as a quarter are transcribed in opero ns.