Twintron
Encyclopedia
Twintrons are intron
s-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. 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. 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. In 2004, several twintrons were discovered in Drosophila
.
Intron
An intron is any nucleotide sequence within a gene that is removed by RNA splicing to generate the final mature RNA product of a gene. The term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts. Sequences that are joined together in the final...
s-within-introns excised by sequential splicing
RNA splicing
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...
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
Group II intron
Group II introns are a large class of self-catalytic ribozymes as well as mobile genetic element found within the genes of all three domains of life. Ribozyme activity can occur under high-salt conditions in vitro. However, assistance from proteins is required for in vivo splicing...
within another group II intron in Euglena chloroplast
Chloroplast
Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...
genome. 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
Group III intron
Group III intron is a class of introns found in mRNA genes of chloroplasts in euglenoid protists. They have a conventional group II-type dVI with a bulged adenosine, a streamlined dI, no dII-dV, and a relaxed splice site consensus. Splicing is by two transesterification reactions with a dVI bulged...
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. 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. In 2004, several twintrons were discovered in Drosophila
Drosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
.