This family represents the SL1 RNA. SL1 is commonly located in the spacer region between 5S-rRNA genes where it is involved in trans-splicing. Trans-splicing is a form of RNA processing. The acquisition of a spliced leader from an SL RNA is an intra-molecular reaction which precisely joins exons derived from separately transcribed RNAs. This mechanism of mRNA maturation has been shown to occur in a number of lower eukaryotes and is commonplace in nematodes.