U5 RNA is a non-coding RNA that is a component of both types of known spliceosome. The precise function of this molecule is unknown, though it is known that the 5' loop is required for splice site selection and p220 binding, and that both the 3' stem-loop and the Sm site are important for Sm protein binding and cap methylation.
^Hinz M, Moore MJ, Bindereif A (August 1996). "Domain analysis of human U5 RNA. Cap trimethylation, protein binding, and spliceosome assembly". J. Biol. Chem. 271 (31): 19001–19007. doi:10.1074/jbc.271.31.19001. PMID8702566.