Twintron

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Twintrons are introns-within-introns excised by sequential splicing reactions. Twintrons are presumably formed by the insertion of a mobile intron into an existing intron.

Twintron was discovered by Donald W. Copertino and Richard B. Hallick as a group II intron within another group II intron in Euglena chloroplast genome.[1] They found that splicing of both the internal and external introns occurs via lariat intermediates. Additionally, twintron splicing was found to proceed by a sequential pathway, the internal intron being removed prior to the excision of the external intron.

Since the original discovery, there have been other reports of Group III twintrons and GroupII/III twintrons in Euglena gracilis chloroplast. In 1993 a new type of complex twintron composed of four individual group III introns has been characterized.[2] The external intron was interrupted by an internal intron containing two additional introns. In 1995 scientists discovered the first non-Euglena twintron in cryptomonad alga Pyrenomonas salina.[3] In 2004, several twintrons were discovered in Drosophila.[4]

References

  1. ↑ Copertino DW, Hallick RB (February 1991). "Group II twintron: an intron within an intron in a chloroplast cytochrome b-559 gene". The EMBO Journal 10 (2): 433–42. PMC 452664. PMID 1899376. 
  2. ↑ Drager RG, Hallick RB (May 1993). "A complex twintron is excised as four individual introns". Nucleic Acids Research 21 (10): 2389–94. doi:10.1093/nar/21.10.2389. PMC 309537. PMID 7685079. 
  3. ↑ Maier UG, Rensing SA, Igloi GL, Maerz M (January 1995). "Twintrons are not unique to the Euglena chloroplast genome: structure and evolution of a plastome cpn60 gene from a cryptomonad". Molecular & General Genetics 246 (1): 128–31. doi:10.1007/BF00290141. PMID 7823908. 
  4. ↑ Scamborova P, Wong A, Steitz JA (March 2004). "An intronic enhancer regulates splicing of the twintron of Drosophila melanogaster prospero pre-mRNA by two different spliceosomes". Molecular and Cellular Biology 24 (5): 1855–69. doi:10.1128/MCB.24.5.1855-1869.2004. PMC 350559. PMID 14966268. 
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