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词条 Group III intron
释义

  1. Discovery and identification

  2. References

  3. See also

  4. External links

{{Short description|Genetic intron in some protists}}Group III intron is a class of introns found in mRNA genes of chloroplasts in euglenid 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.[1]{{rp|at=fig. 2}} Splicing is done with two transesterification reactions with a dVI bulged adenosine as initiating nucleophile; the intron is excised as a lariat.[2] Not much is known about how they work,[1] although an isolated chloroplast transformation system has been constructed.[2]

Discovery and identification

In 1984, Montandon and Stutz reported examples of a novel type of introns in Euglena chloroplast.[3] In 1989, David A. Christopher and Richard B. Hallick found a few more examples and proposed the name "Group III introns" to identify this new class with the following characteristics:[4]

  • Group III introns are much shorter than other self-splicing intron classes, ranging from 95 to 110 nucleotides amongst those known to Christopher and Hallick, and identified in chloroplasts. On the other hand, Christopher and Hallick stated: "By contrast, the smallest Euglena chloroplast group II intron ... is 277 nucleotides."[4]
  • Their conserved sequences proximal to the splicing sites have similarities to those of group II introns, but have fewer conserved positions.
  • They do not map into the conserved secondary structure of group II introns. (Indeed, Christopher and Hallick were unable to identify any conserved secondary structure elements among group III introns.)
  • They are usually associated with genes involved in translation and transcription.
  • They are very A+T rich.

In 1994, discovery of a group III intron with a length of one order of magnitude longer indicated that length alone is not the determinant of splicing in Group III introns.[5]

Splicing of group III introns occurs through lariat and circular RNA formation.[5] Similarities between group III and nuclear introns include conserved 5' boundary sequences, lariat formation, lack of internal structure, and ability to use alternate splice boundaries.[1]

References

1. ^1 2 {{cite journal |vauthors=Copertino DW, Hallick RB |title=Group II and group III introns of twintrons: potential relationships with nuclear pre-mRNA introns |journal=Trends Biochem. Sci. |volume=18 |issue=12 |pages=467–71 |date=December 1993 |pmid=8108859 |doi= 10.1016/0968-0004(93)90008-b|url=}}
2. ^{{cite journal |last1=Doetsch |first1=NA |last2=Favreau |first2=MR |last3=Kuscuoglu |first3=N |last4=Thompson |first4=MD |last5=Hallick |first5=RB |title=Chloroplast transformation in Euglena gracilis: splicing of a group III twintron transcribed from a transgenic psbK operon. |journal=Current genetics |date=February 2001 |volume=39 |issue=1 |pages=49-60 |doi=10.1007/s002940000174 |pmid=11318107}}
3. ^{{cite journal |vauthors=Montandon PE, Stutz E |title=Nucleotide sequence of a Euglena gracilis chloroplast genome region coding for the elongation factor Tu; evidence for a spliced mRNA |journal=Nucleic Acids Res. |volume=11 |issue=17 |pages=5877–92 |date=September 1983 |pmid=6310519 |pmc=326324 |doi= 10.1093/nar/11.17.5877|url=http://nar.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=6310519}}
4. ^1 {{cite journal |vauthors=Christopher DA, Hallick RB |title=Euglena gracilis chloroplast ribosomal protein operon: a new chloroplast gene for ribosomal protein L5 and description of a novel organelle intron category designated group III |journal=Nucleic Acids Res. |volume=17 |issue=19 |pages=7591–608 |date=October 1989 |pmid=2477800 |pmc=334869 |doi= 10.1093/nar/17.19.7591|url=http://nar.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=2477800}}
5. ^1 2 {{cite journal|author1=Donald W. Copertino DW |author2=Hall ET |author3=Van Hook FW |author4=Jenkins KP |author5=Hallick RB |title=A group III twintron encoding a maturase-like gene excises through lariat intermediates |journal=Nucleic Acids Res. |volume=22 |issue=6 |pages=1029–36 |year=1994 |pmid=7512259 |url=http://nar.oxfordjournals.org/cgi/reprint/22/6/1029|doi=10.1093/nar/22.6.1029|pmc=307926}}

See also

  • Twintron

External links

  • GO:0000374 - Gene ontology entry for Group III intron splicing
{{DEFAULTSORT:Group Iii Intron}}

3 : RNA|Ribozymes|RNA splicing
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