The IS3/IS481-like insertion sequences (ISs) described in prokaryotes and certain protists (Fayet et al. 1990; Capy et al. 1997), which encode for a single transposase product of 400-600 residues with no HHCC module (for simplicity´s sake the figure below shows the genomic structure without introns).
The name “IS3/IS481”-like has been taken from the description provided by Bao et al. 2010. There are two complementary classifications for IS3/IS481-like ISs. Based on sequence these enzymes can be classified as DDE transposases (TRs) and integrases (INTs). In fact, the hypothesis of common ancestry among DDE TRs and INTs originally derives from the elucidation of convincing similarity between LTR retroelement INTs and IS3/IS481-like ISs (Fayet et al. 1990; Capy et al. 1997). Based on INT-like structural potential similarities, IS3/IS481-like ISs are however 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.