The extra leader sequence is found in an abundant 94 nt transcript. The small RNA has a 2,2,7 trimethylguanosine cap, characteristic of snRNAs, is associated with spliceosomes and is an RNA polymerase III transcription product. Other Pages Interpretations mRNAs in C. elegans and T. brucei are provided 5' caps by trans-splicing from the 94 nt transcript. Note that the RNA polymerase III cap differs in structure from the RNA polymerase II transcript's caps. In these cases, although the mRNA is monocistronic, the nuclear transcript was polycistronic .
Caps are important for initiation of translation.
Nucleotides may also be added to the 3' ends of RNAs.