Tor4 is a Ty3/Gypsy lineage of putative retroviruses and LTR retrotransposons described with a wide number of copies, together with three other Ty3/Gypsy retroelement clades, in the miniature genome of the tunicate Oikopleura dioica (Volff et al. 2004). The full-length genome of Tor4a (taken as a representative LTR retrotransposon) is 6.8 Kb in size (including two described LTRs with no apparent homology each other). The internal region of this element contains a Primer Binding Site (PBS), coding region and Polypurine Tract (PPT). The coding region displays two ORFs encoding for the gag and pol polyprotein domains typical of LTR retrotransposons (Volff et al. 2004).
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