Excisions of the Ikirara1 transposon in an Anopheles gambiae cell line

In order to determine whether there are active genomic copies of the Anopheles gambiae transposon Ikirara, we developed an excision assay based on an internally deleted copy, Ikirara1. This element has 216 bp perfect inverted repeats at its termini, apparently caused a duplication of the dinucleotide TA at its insertion site between vitellogenin genes, and is thought to have been inserted recently at this location. The firefly luciferase gene on the E. coli tac promoter was inserted into Ikirara1 and used as a reporter to assess whether activities in an A. gambiae cell line could cause Ikirara excision. Excisions were observed at a rate of 0.038% in these experiments, but none was detected in controls. The five independent excision products examined gave identical sequences. Excisions were nearly precise, but left behind a footprint of 15 bp of the 3' inverted repeat of Ikirara1 between duplicated TAs. These excisions can be explained by a mechanism formally similar to that proposed for excision of mariner/Tc1 elements with cuts at the transposon ends staggered by 15 bases.