Abstract
The frequency of transposition of Tnlac to pGC200, an IncFII R plasmid, increased during the storage of the host [Escherichia coli] strain. This result is explained by the fact that the transpositional event is temperature-dependent: it occurred readily when the host strain was grown at 30.degree. C but it was nearly undetectable when the host strain was grown and kept at 37.degree. C. Fusions between 2 different plasmids carrying Tnlac with pGC200 were also thermosensitive, suggesting a relation between cointegrate formation and transposition. Lactose did not influence the frequency of transposition of Tnlac.