Trans-splicing is a special form of RNA processing

Messenger RNA

Messenger RNA is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcribed from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes. Here, the nucleic acid polymer is translated into a polymer of amino acids: a protein...

 in eukaryote

Eukaryote

A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...

s where exon

Exon

An exon is a nucleic acid sequence that is represented in the mature form of an RNA molecule either after portions of a precursor RNA have been removed by cis-splicing or when two or more precursor RNA molecules have been ligated by trans-splicing. The mature RNA molecule can be a messenger RNA...

s from two different primary RNA transcripts are joined end to end and ligated

Ligase

In biochemistry, ligase is an enzyme that can catalyse the joining of two large molecules by forming a new chemical bond, usually with accompanying hydrolysis of a small chemical group dependent to one of the larger molecules...

.

In contrast "normal" (cis-)splicing

Splicing (genetics)

In molecular biology and genetics, splicing is a modification of an RNA after transcription, in which introns are removed and exons are joined. This is needed for the typical eukaryotic messenger RNA before it can be used to produce a correct protein through translation...

 processes a single molecule. That is, trans-splicing results in an RNA transcript that came from multiple RNA polymerases on the genome. This phenomenon can be exploited for molecular therapy to address mutated gene products.

Trans-splicing can be the mechanism behind certain oncogenic fusion transcript

Fusion transcript

Fusion transcript is a chimeric RNA encoded by a fusion gene or by two different genes by subsequent trans-splicing. Certain fusion transcripts are commonly produced by cancer cells, and detection of fusion transcripts is part of routine diagnostics of certain cancer types....

s.

Trans-splicing is used by certain microbial organisms, notably protozoa of the Kinetoplastae class

Kinetoplastid

The kinetoplastids are a group of single-cell flagellate protozoa, including a number of parasites responsible for serious diseases in humans and other animals, as well as various forms found in soil and aquatic environments...

to produce variable surface antigens and change from one life stage to another.