MOBILIZATION OF QUIET, ENDOGENOUS TC3 TRANSPOSONS OF CAENORHABDITIS-ELEGANS BY FORCED EXPRESSION OF TC3 TRANSPOSASE

The commonly studied Caenorhabditis elegans strain Bristol N2 contains approximately 15 copies per genome of the transposon Tc3. However, Tc 3 is not active in Bristol N2. Tc3 contains one major open reading fra me (Tc3A). We have fused this open reading frame to an inducible promo ter and expressed it in a transgenic Bristol N2 line. Tc3A expression resulted in frequent excision and transposition of endogenous Tc3 elem ents. This shows that the Bristol N2 genome contains Tc3 transposons t hat are cis proficient for transposition, but are immobile because Tc3 A is absent. We demonstrate that recombinant Tc3A binds specifically t o the terminal nucleotides of the Tc3 inverted repeat, indicating that Tc3A is the Tc3 transposase. Activation of Tc3 transposition in vivo was accompanied by the appearance of extrachromosomal, linear copies o f Tc3. These may be intermediates in Tc3 transposition.