CHARACTERIZATION OF THE TN5 TRANSPOSASE AND INHIBITOR PROTEINS - A MODEL FOR THE INHIBITION OF TRANSPOSITION

Tn5 is a composite transposon consisting of two IS50 sequences in inve rted orientation with respect to a unique, central region encoding sev eral antibiotic resistances. The IS50R element encodes two proteins in the same reading frame which regulate the transposition reaction: the transposase (Tnp), which is required for transposition, and an inhibi tor of transposition (Inh). The inhibitor is a naturally occurring del etion variant of Tnp which lacks the N-terminal 55 amino acids. In thi s report, we present the purification of both the Tnp and Inh proteins and an analysis of their DNA binding properties. Purified Tnp, but no t Inh, was found to bind specifically to the outside end of Tn5. Inh, however, stimulated the binding activity of Tnp to outside-end DNA and was shown to be present with Tnp in these bound complexes. Inh was al so found to exist as a dimer in solution. These results indicate that the N-terminal 55 amino acids of Tnp are required for sequence-specifi c binding. They also suggest that Inh inhibits transposition by formin g mixed oligomers with Tnp which still bind to the ends of the transpo son but are defective for later stages of the transposition reaction.