Journal Article

A New Class of LINEs (<i>ATLN-L</i>) from <i>Arabidopsis thaliana</i> with Extraordinary Structural Features

Kenichi Noma, Hisako Ohtsubo and Eiichi Ohtsubo

in DNA Research

Published on behalf of Kazusa DNA Research Institute

Volume 8, issue 6, pages 291-299
Published in print January 2001 | ISSN: 1340-2838
Published online January 2001 | e-ISSN: 1756-1663 | DOI: http://dx.doi.org/10.1093/dnares/8.6.291

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The Arabidopsis thaliana genome has about 250 copies of LINEs (here called ATLNs). Of these, some, called ATLN-Ls, have an extra sequence of about 2 kb in the region downstream of two consecutive open reading frames, orf1 and orf2. Interestingly, the extra sequences in these ATLN-L members have another open reading frame, designated as orf3. Each member is flanked by direct repeats of a target site sequence, showing that ATLN-L members with the three open reading frames have retrotransposed as a unit. The ATLN-L members are also distinct from other ATLN members: orf1 terminates with TAA (or TAG) and is located in the same frame as orf2, and the ATG initiation codon of orf2 is not present in the proximal region. A sequence that may form a pseudoknot structure in ATLN-L mRNA was present in the proximal region of orf2, therefore the TAA (or TAG) termination codon of orf1 is assumed to be suppressed to produce an Orf1-Orf2 transframe protein during the translation of the ATLN-L mRNA. The region between orf2 and orf3 is several hundred bp long, suggesting that orf3 expression is independent of orf1-orf2. The amino acid sequences of the proteins Orf1 and Orf3 are highly homologous in their N-terminal half regions that have a retroviral zinc-finger motif for RNA binding. Orf3, however, has a leucine-zipper motif in addition to the zinc-finger motif. The C-terminal regions of the Orf1 and Orf3 proteins have poor homology, but seem to have nuclear localization signals, suggesting that these proteins are involved in the transfer of ATLN-L mRNA to nuclei. A phylogenetic tree shows that Orf3 proteins form a branch distinct from the branches of the Orf1 proteins encoded by ATLN-L members. This indicates that an ancestor element of ATLN-Ls has incorporated the orf1 frame carried by another ATLN member into its distal region to orf1-orf2 during evolution.

Keywords: Arabidopsis thaliana; non-LTR retrotransposon (LINE); pseudoknot structure; leucine-zipper motif; translational control; nuclear localization signal

Journal Article.  0 words. 

Subjects: Genetics and Genomics

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