OPERONS IN C-ELEGANS - POLYCISTRONIC MESSENGER-RNA PRECURSORS ARE PROCESSED BY TRANSSPLICING OF SL2 TO DOWNSTREAM CODING REGIONS

The MRNAs of six C. elegans genes are known to be trans-spliced to SL2 . We report here that a similarly oriented gene is located 100-300 bp upstream of each. We present evidence that the genes in these clusters are cotranscribed and downstream mRNAs are formed by cleavage at the polyadenylation site and trans-splicing. From one three-gene cluster w e isolated cDNA clones representing both polycistronic RNAs and mRNAs polyadenylated at the free 3' end created by trans-splicing, suggestin g that polycistronic RNAs can be processed by trans-splicing. Several experiments indicate that SL2 trans-splicing is a consequence of a gen e's downstream location in an operon. In particular, when an SL1-accep ting gene was moved to a downstream location, its mRNA was trans-splic ed largely to SL2. The possible regulatory significance of cotranscrip tion of C. elegans genes is discussed.