Active gypsy/Ty3 retrotransposons or retroviruses in Caenorhabditis elegans

A gypsy/Ty3-class retrotransposon (Cer1) is integrated in the DNA of Caenorhabditis elegans chromosome III. It is 8865 nt in length and has 492-nt long terminal repeats that are identical in DNA sequence. There is an exceptionally long (6819 nt) open reading frame uninterrupted by frame-shift mutations in the period since the insertion, which must therefore have been rather recent. Alignment with other gypsy-class elements and with retroviruses indicates that an env gene occupies the 3' 1.2 kb of the open reading frame. A search through GenBank has uncovered two additional gypsy-class elements from C. elegans that are very closely related in DNA sequence to this insert and are transcribed. Since gypsy of Drosophila has been shown to be an infectious element, it is possible that retrovirus-like gypsy elements are active in C. elegans.