Tribel is a LTR retrotransposon found in the genome of the insect “red flour beetle” Tribolium castaneum (Llorens et al. 2009). Its name is an acronym derived from “Tribolium castaneum Bel/Pao element”. Tribel belongs to the Bel clade (Copeland et al. 2005) within Branch 1 of the Bel/Pao family (Llorens et al. 2009).
The genome of Tribel is about of 6 Kb in size (5957 bp long), including LTRs of 284 nt. The internal region of this element contains three ORFs encoding for the gag and pol polyproteins. The largest ORF (897aa) contains both potential gag and pol domains: three putative Cys-motifs characteristic of the gag associated nucleocapsid domain of Bel/Pao LTR retrotransposons, and the pol protease and the N-terminal region of the reverse transcriptase domains. The second ORF (334aa) presents the remaining part of reverse transcriptase and the RNase H domains, the last ORF (373aa) codes for the integrase pol domain (Llorens et al. 2009).
Figure not to scale. If present, long terminal repeats (LTRs) have been highlighted in blue. Amino acid motifs noted with lines indicate the conserved residues in each protein domain, abbreviations below mean:
|DU or DUT=dUTPase
|TAV or IBMP=transactivator/viroplasmin or inclusion body matrix protein
|PBS=primer binding site
|ATF=aphid transmission factor
|VAP=virion associated protein