Open AccessThe 5′ Untranslated Region and Gag product of Idefix, a Long Terminal Repeat-Retrotransposon from Drosophila melanogaster, Act Together To Initiate a Switch between Translated and Untranslated States of the Genomic mRNA
Author(s) -
Carine Meignin,
JeanLuc Bailly,
Frédérick Arnaud,
B. Dastugue,
Chantal Vaury
Publication year - 2003
Publication title -
molecular and cellular biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.14
H-Index - 327
eISSN - 1067-8824
pISSN - 0270-7306
DOI - 10.1128/mcb.23.22.8246-8254.2003
Subject(s) - biology , retrotransposon , untranslated region , internal ribosome entry site , genetics , drosophila melanogaster , cistron , start codon , five prime untranslated region , long terminal repeat , upstream open reading frame , primer binding site , gene , translation (biology) , messenger rna , rna , gene expression , reverse transcriptase , transposable element , genome
Idefix is a long terminal repeat (LTR)-retrotransposon present in Drosophila melanogaster which shares similarities with vertebrates retroviruses both in its genomic arrangement and in the mechanism of transposition. Like in retroviruses, its two LTRs flank a long 5' untranslated region (5'UTR) and three open reading frames referred to as the gag, pol, and env genes. Here we report that its 5'UTR, located upstream of the gag gene, can fold into highly structured domains that are known to be incompatible with efficient translation by ribosome scanning. Using dicistronic plasmids analyzed by both (i) in vitro transcription and translation in rabbit reticulocyte or wheat germ lysates and (ii) in vivo expression in transgenic flies, we show that the 5'UTR of Idefix exhibits an internal ribosome entry site (IRES) activity that is able to promote translation of a downstream cistron in a cap-independent manner. The functional state of this novel IRES depends on eukaryotic factors that are independent of their host origin. However, in vivo, its function can be down-regulated by trans-acting factors specific to tissues or developmental stages of its host. We identify one of these trans-acting factors as the Gag protein encoded by Idefix itself. Our data support a model in which nascent Gag is able to block translation initiated from the viral mRNA and thus its own translation. These data highlight the fact that LTR-retrotransposons may autoregulate their replication cycle through their Gag production.