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Behavior of transposon Tn1 in Proteus mirabilis

Vanda D. de Magalhaes^I; Sérgio Olavo P. da Costa^II

^IDepartamento de Bioquímica, Instituto de Química, Universidade de São Paulo, Caixa Postal 20780, 01498 São Paulo, Brasil
^IIDepartamento de Biologia, Instituto de Biociências, Universidade de São Paulo, Caixa Postal 11461, 05499 São Paulo, Brasil. Send correspondence to S.O.P.C.

ABSTRACT

The Tnl transposition frequency from plasmid pTH10 to the host chromosome was higher when the host was Proteus mirabilis than when it was Escherichia coli. Moreover it is possible that the values obtained for P. mirabilis were underestimated since the transposon donor plasmid is unstable in the P. mirabilis strain PG1342. Hybridization experiments suggested that there are more than one insertion per chromosome of P. mirabilis but further analyses are required to localize the insertion. If Tnl elects a hot-spot to insert into the host chromosome this target does not cause auxotrophy when disrupted by Tnl insertion in the clones tested.
Transposition to plasmids harbored by P. mirabifis does not always happen at higher levels than to the chromosome as has been reported for E. colt. Furthermore the frequencies of Tnl insertions are variable depending on the target DNA. The selection of an insertion site was different forP. mirabilis and E. colt suggesting that host factors play an important role on this selection. On the other hand, Tnl showed preferential insertion into another transposon (Tn402) independent of the host. Tnl insertion is not stable in the latter case leading to excision of the ampicillin transposon.

Keywords: Transposon tn1; Proteus mirabilis.

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