Trans-splicing is a special form of RNA processing in eukaryotes where exons from two different primary RNA transcripts are joined end to end and ligated.
Whereas "normal" (cis-)splicing processes a single molecule, trans-splicing generates a single RNA transcript from multiple separate pre-mRNAs. This phenomenon can be exploited for molecular therapy to address mutated gene products.
Trans-splicing can be the mechanism behind certain oncogenic fusion transcripts.
Trans-splicing is used by certain microbial organisms, notably protozoa of the Kinetoplastae class to express genes. In these organisms, a capped splice leader RNA is transcribed; simultaneously, genes are transcribed in long polycistrons. The capped splice leader is trans-spliced onto each gene to generate monocistronic capped and polyadenylated transcripts.