Intron-mediated enhancement (IME) is the ability of an

intron An intron is any nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word ''intron'' is derived from the term ''intragenic region'', i.e., a region inside a gene."The notion of the cistron .e., gen ...

sequence to enhance the expression of a

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

containing that intron. In particular, the intron must be present in the transcribed region of the gene for enhancement to occur, differentiating IME from the action of typical transcriptional enhancers. Descriptions of this phenomenon were first published in cultured

maize Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout grass that produces cereal grain. It was domesticated by indigenous peoples in southern Mexico about 9,000 years ago from wild teosinte. Native American ...

cells in 1987, and the term "intron-mediated enhancement" was subsequently coined in 1990. A number of publications have demonstrated that this phenomenon is conserved across

eukaryote The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...

s, including humans, mice, ''

Arabidopsis ''Arabidopsis'' (rockcress) is a genus in the family Brassicaceae. They are small flowering plants related to cabbage and mustard. This genus is of great interest since it contains thale cress (''Arabidopsis thaliana''), one of the model organ ...

'', rice, and '' C. elegans.'' However, the mechanism(s) by which IME works are still not completely understood. When testing to see whether any given intron enhances the expression of a gene, it is typical to compare the expression of two constructs, one containing the intron and one without it, and to express the difference between the two results as a " fold increase" in enhancement. Further experiments can specifically point to IME as the cause of expression enhancement - one of the most common is to move the intron upstream of the transcription start site, removing it from the transcript. If the intron can no longer enhance expression, then inclusion of the intron in the transcript is important, and the intron probably causes IME. Not all introns enhance gene expression, but those that do can enhance expression between 2– and >1,000–fold relative to an intronless control. In ''Arabidopsis'' and other plant species, th
IMEter
has been developed to calculate the likelihood that an intron sequence will enhance gene expression. It does this by calculating a score based on the patterns of

nucleotide Nucleotides are Organic compound, organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both o ...

sequences within the target sequence. The position of an intron within the transcript is also important - the closer an intron is to the start (5' end) of a transcript, the greater its enhancement of gene expression.

References

{{DEFAULTSORT:Intron-Mediated Enhancement Gene expression