Characterization of the Caenorhabditis elegans Tc1 transposase in vivo and in vitro.

We have investigated the function of the Tc1A gene of the mobile element Tc1 of Caenorhabditis elegans. Tc1 is a member of a family of transposons found in several animal phyla, such as nematodes, insects, and vertebrates. Two lines of evidence show that Tc1A encodes the transposase of Tc1. First, forced expression of the Tc1A protein in transgenic nematodes results in an enhanced level of transposition of endogenous Tc1 elements. Second, DNase I footprinting and gel retardation assays show that Tc1A binds specifically to the inverted repeats at the ends of the element and that the Tc1A recognition site is located between base pairs 5 and 26 from the ends of Tc1. Functional dissection of the transposase shows the presence of two distinct DNA-binding domains. A site-specific DNA-binding domain is contained within the amino-terminal 63 residues of Tc1A; this region shows sequence similarity to the prokaryotic IS30 transposase. A second, general DNA-binding domain is located between amino acids 71 and 207. Our results suggest that Tc1 is more similar to prokaryotic insertion elements than to eukaryotic transposons such as P elements in Drosophila or Ac and En-1 in plants.