Nb. Delacruz et al., CHARACTERIZATION OF THE TN5 TRANSPOSASE AND INHIBITOR PROTEINS - A MODEL FOR THE INHIBITION OF TRANSPOSITION, Journal of bacteriology, 175(21), 1993, pp. 6932-6938
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.