Intercistronic region required for polycistronic Pre-mRNA processing in Caenorhabditis elegans

In Caenorhabditis elegans, polycistronic pre-mRNAs are processed by cleavag e and polyadenylation at the 3' ends of the upstream genes and trans splici ng, generally to the specialized spliced leader SL2, at the 5' ends of the downstream genes. Previous studies have indicated a relationship between th ese two events in the processing of a heat. shock-induced gpd-2-gpd-3 polyc istronic pre-mRNA, Here, we report mutational analysis of the intercistroni c region of this operon by linker scan analysis, Surprisingly, no sequences downstream of the 3' end were important for 3'-end formation. In contrast, a U-rich (Ur) element located 29 bp downstream of the site of 3'-end forma tion was shown to be important for downstream mRNA biosynthesis. This simil ar to 20-bp element is sufficient for SL2 trans splicing and mRNA accumulat ion when transplanted to a heterologous context. Furthermore, when the down stream gene was replaced by a gene from another organism, no loss of trans- splicing specificity was observed, suggesting that the Ur element may be th e primary signal required for downstream mRNA processing.