Some trans-spliced snRNAs have been observed to have a N,N,7-trimethylguanosine cap. This particular modification to the guanosine cap is rare in snRNAs. Trans-splicing is a phenomenon in which exons from two different primary RNA transcripts are ligated together. These rare variants have been seen during development in C.elegans and are associated with polysomes. How this modification is regulated in certain cell types and the exact function of this modification remains largely unknown, although it has been speculated that this modification may help define a special subset of trimethylguanosine-regulated RNAs.