Cer1 is a Ty3/Gypsy LTR retroelement originally characterized as an integrate of the chromosome III of Caenorhabditis elegans (Britten 1995; Bowen and McDonald 1999). To date, no other homologues of Cer1 have been described. However, phylogenetic analyses based on both gag and pol polyproteins suggest that Cer1 might be a distantly related of Cer2-3 clade (see gag-pro-pol tree in section "phylogenies"). The genomic structure of Cer1 is 8.9 Kb in size including LTRs of 492 nt. The internal region of this element displays a Primer Binding Site (PBS) complementary to a tRNA Lys-Pro, a single Open Reading Frame (ORF) coding for a gag-pol polyprotein, and a Polypurine Tract (PPT) adjacent to the 3′LTR (Britten 1995). Cer1 also presents C-terminal and in frame with the integrase domain, an env-like domain already under study (Britten 1995).
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