An interrupted gene (also called a

split gene An interrupted gene (also called a split gene) is a gene that contains expressed regions of DNA called exons, split with unexpressed regions called introns (also called intervening regions). Exons provide instructions for coding proteins, which c ...

) is a gene that contains expressed regions of DNA called

exon An exon is any part of a gene that will form a part of the final mature RNA produced by that gene after introns have been removed by RNA splicing. The term ''exon'' refers to both the DNA sequence within a gene and to the corresponding sequen ...

s, split with unexpressed regions called

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., gene. ...

s (also called intervening regions). Exons provide instructions for coding proteins, which create

mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein. mRNA is ...

necessary for the synthesis of

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

s. Introns are removed by recognition of the donor site (5' end) and the splice acceptor site (3' end). The architecture of the interrupted gene allows for the process of

alternative splicing Alternative splicing, or alternative RNA splicing, or differential splicing, is an alternative splicing process during gene expression that allows a single gene to code for multiple proteins. In this process, particular exons of a gene may be ...

, where various mRNA products can be produced from a single gene. The function of introns are still not fully understood and are called noncoding or junk DNA.

Discovery

Interrupted genes were independently discovered by

Richard J. Roberts Sir Richard John Roberts (born 6 September 1943) is a British biochemist and molecular biology, molecular biologist. He was awarded the 1993 Nobel Prize in Physiology or Medicine with Phillip Allen Sharp for the discovery of introns in eukaryo ...

and

Phillip A. Sharp Phillip Allen Sharp (born June 6, 1944) is an American geneticist and molecular biologist who co-discovered RNA splicing. He shared the 1993 Nobel Prize in Physiology or Medicine with Richard J. Roberts for "the discovery that genes in euka ...

in 1977, for which they shared the 1993 Nobel Prize in Physiology or Medicine. Their discovery implied the existence of then-unknown machinery for splicing out introns and assembling genes; namely, the

spliceosome A spliceosome is a large ribonucleoprotein (RNP) complex found primarily within the nucleus of eukaryotic cells. The spliceosome is assembled from small nuclear RNAs (snRNA) and numerous proteins. Small nuclear RNA (snRNA) molecules bind to specifi ...

. Unlike prokaryotic genomes, eukaryotic genomes were largely complex and inconsistent. It was soon accepted that 94% of human genes are interrupted, and 50% of hereditary diseases are involved in splicing intron errors out of interrupted genes. The best known example of a disease caused by a splicing error is

Beta-thalassemia Beta thalassemias (β thalassemias) are a group of inherited blood disorders. They are forms of thalassemia caused by reduced or absent synthesis of the beta chains of hemoglobin that result in variable outcomes ranging from severe anemia to cl ...

, in which extra intronic material is erroneously spliced into the gene for making

hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...

Prokaryotes

Unlike eukaryotes,

prokaryote A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...

s have a less complex genome. The structure of prokaryotic genomes contain fewer to none regions of introns and have longer continuous lines of exons, or uninterrupted regions. In other words, they contain more regions of DNA that are expressed. The idea that genome density decreases as the complexity of the organism increases hold true. This is due to the fact that eukaryotes have a much stronger presence of introns than prokaryotes. For example, prokaryotes contain about 1000 genes/Mb while humans contain about 6 genes/Mb. Another example are lower

eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

s, such as

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitut ...

, that have many uninterrupted regions. However, this does not mean that these sections are fully uninterrupted, as

tRNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes), that serves as the physical link between the mRNA and the amino ac ...

synthesis requires excision of a nucleotide sequence, followed by

ligation Ligation may refer to: * Ligation (molecular biology), the covalent linking of two ends of DNA or RNA molecules * In medicine, the making of a ligature (tie) * Chemical ligation, the production of peptides from amino acids * Tubal ligation, a meth ...

. Most bacteria have some interruption of some genes. Interrupted genes are universal in eukaryotes; yeasts may display single interruptions of a minority of genes, while in higher organisms most genes are interrupted. Some eukaryotes may contain multiple interruptions with introns that can be longer than exons. Introns are well-conserved across evolutionary history, suggesting their structure has some importance for the organism. They are longer in advanced organisms (higher plants and animals). Longer growth and development requires longer sequences of gene activation and down-regulation. Details of the role of introns in the regulation of gene accessibility and transcription have yet to be worked out.

References

{{DEFAULTSORT:Interrupted Gene Molecular biology