Tdd-4 and Tdd-5 are two intron-exon structured cut and paste DNA transposons described in the genome of Dictyostelium discoideum (Wells 1999; Glockner et al. 2001). Full-length Tdd-4 and Tdd-5 elements are 3.7 and 3.8 kb respectively, and are flanked by terminal inverted repeats (TIRs) of 260 and 297 nucleotides long (Figure not to scale). For simplicity´s sake the figure below shows the genomic structure without introns.
There are two complementary classifications for the Tdd-like transposons. Based on sequence these elements can be classified as DDE TRs and integrases (INTs). Within this scenario, phylogenetic inference suggests that Tdd-like elements are related to the GINGER2 transposons (Bao et al. 2010) but also to the FOB1 genes and the SCAN/KRAB genes (which are domesticated GINGER2 transposons). Based on INT-like structural potential similarities, the INT coded by Tdd-like transposons are members of the Retroviral Integrase Superfamily (Nowotny 2009) of nucleic acid-processing enzymes involved in; a) selfish evolution; b) replication and repair of DNA; c) recombination and gene fusion; d) RNA-mediated gene silencing; and e) oncogenesis.