Tn1721-encoded resolvase: structure of the tnpR gene and its in vitro functions.

A 760 base pair nucleotide sequence of transposon Tn1721 containing the resolvase (tnpR) gene has been determined. A 186 triplet open reading frame was assigned to tnpR, and the allocation of -35 and -10 promoter boxes was supported by mapping transcription initiation at 70 base pairs upstream of tnpR. Expression of tnpR under tac promoter control generated sufficient resolvase protein for enzyme purification and for in vitro studies. Purified Tn1721 resolvase requires supercoiling and two directly oriented resolution (res) sites. The enzyme resolves cointegrate substrates containing repeat copies of Tn1721 res, of Tn21 res, of Tn21 res/Tn1721 res, but not of Tn3 res.