Characterization of a functional insertion sequence IS from .

BACKGROUND

IS has been suggested as a member of the IS f subgroup in the IS3 family. It encodes a fusion transposase OrfAB produced by programmed - 1 translational frameshifting with two overlapping reading frames and . To better characterize IS, the binding and cleaving activities of the IS transposase and its transposition frequency were studied.

RESULTS

The purified IS transposase OrfAB was a functional protein in vitro since it bound specifically to IS terminal inverted repeat sequences (IRs) and cleaved the transposon ends at the artificial mini-transposon pUC19-IRL-gfp-IRR. In addition, the transposition frequency of IS in vivo was approximately 1.76 ± 0.13 × 10, based on a GFP hop-on assay. Furthermore, OrfB cleaved IRs with the similar catalytic activity of OrfAB, while OrfA had no catalytic activity. Finally, either OrfA or OrfB significantly reduced the transposition of IS induced by OrfAB.

CONCLUSION

We have confirmed that IS is a member of IS/IS family. The IS transposase OrfAB could bind to and cleave the specific fragments containing the terminal inverted repeat sequences and induce the transposition, suggesting that IS is at least partially functional. Meanwhile, both OrfA and OrfB inhibited the transposition by IS. Our results will help understand biological roles of IS in its host .