Two naturally occurring transposons indistinguishable from Tn7.

Two plasmids from different sources, determining trimethoprim and streptomycin resistances, harbour transposons which we designate Tn71 and Tn72. These transposons are indistinguishable from Tn7 in the resistances determined, in their molecular masses and in the number and relative positions of their sites susceptible to the restriction enzymes EcoRI, HindIII and BamHI. We conclude that Tn7 has been naturally spread among plasmids.