trans-spliced Caenorhabditis elegans mRNAs retain trimethylguanosine caps.

The nematode Caenorhabditis elegans has an unusual small nuclear RNA, containing a 100-nucleotide RNA molecule, spliced leader RNA, which donates its 5' 22 nucleotides to a variety of recipient RNAs by a trans-splicing reaction. The spliced leader RNA has a 5' trimethylguanosine (TMG) cap, which becomes the 5' end of trans-spliced mRNAs. We found that mature trans-spliced mRNAs were immunoprecipitable with anti-TMG cap antibodies and that TMG-containing dinucleotides specifically competed with the trans-spliced mRNAs for antibody binding. We also found that these mRNAs retained their TMG caps throughout development and that the TMG-capped mRNAs were polysome associated. Since the large majority of C. elegans mRNAs are not trans-spliced, the addition of the spliced leader and its TMG cap to a limited group of recipient RNAs may create a functionally distinct subset of mRNAs.