Long interspersed nuclear element

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Under LINE s (Abbr. ENGL. Long interspersed nuclear element ) is meant typically 6 to 8 kbp long, repeated frequently, and relatively freely distributed DNA sequences in the genome . LINEs belong to the transposable elements that use a ribonucleic acid (RNA) as an intermediate stage ( retro element ) and do not have a long terminal repeat , but rather multiply through retrotransposition (see retroposon , although these do not count among the non-LTR retrotransposons). They have genes for two proteins : one for binding and transporting RNA and one with activity for a reverse transcriptase and for an endonuclease .

LINEs are mainly found in AT-rich regions in heterochromatin , or in the G bands on chromosomes treated with Giemsa staining , see also life cycle. In humans, LINEs make up just over 20% of the total genome; common elements are LINE-1, LINE-2 and LINE-3.

Life cycle of the LINE-1

The L1 has genes for two proteins: one that binds RNA (p40) and one that has both reverse transcriptase and endonuclease activity (p150). The special thing is that the promoter for the transcription is located in the 5'-UTR of the LINE, ie "inside".

The internal promoter triggers the transcription by the RNA polymerase II of itself and the two proteins. After translation , the proteins encoded by the mRNA are attached to the mRNA. The endonuclease cuts in a target sequence in the DNA (often an oligo (dT)) and thus generates a free 3'-OH, which in turn serves as a primer for reverse transcription. The oligo (A) tail (function of the poly (A) tail ) attaches to this oligo (T) , with which the LINE mRNA can serve as a template. Often the reverse transcriptase does not migrate to the 5 'end of the LINE template, but breaks off earlier, which is why only a small part of the L1 in the genome is still capable of jumping.

How the integration and synthesis of the second strand takes place is still unclear.

See also

Individual evidence

  1. ↑ Tania A. Baker, Stephen P. Bell, Alexander Gann, Michael Levine, Richard Losick, James D. Watson: Watson Molecular Biology . 2010, ISBN 978-3-86894-029-9 ( page 404 in the Google book search).
  2. ↑ a b c Werner Buselmaier: Biology for medical professionals . Springer, 2006, ISBN 978-3-540-29374-3 ( page 206 in the Google book search).
  3. ↑ Lander ES, Linton LM, Birren B, et al. : Initial sequencing and analysis of the human genome . In: Nature . 409, No. 6822, February 2001, pp. 860-921. doi : 10.1038 / 35057062 . PMID 11237011 .