Summary: A tetracycline resistance (Tc) determinant from strain 630 was cloned into the plasmid vector pUC13. The resulting plasmid pPPM20, containing an insert of 3.4 kbp, was mapped and a 1.1 kbp I-III fragment wholly within the Tc gene was identified. Dot-blot hybridization studies with the 1.1 kbp fragment showed that the Tc gene belonged to hybridization class M. Tc could be transferred between strains and to at a frequency of 10 per donor cell. The element could be returned from to at a frequency of 10 per donor cell. This is the first demonstration of acting as a recipient in intergeneric crosses. DNA from transconjugants digested with RV always has two hybridizing fragments of 9.5 and 11.0 kbp when probed with pPPM20. DNA from transconjugants digested with RV produced one hybridizing band of variable size when probed with pPPM20. The behaviour of the element was reminiscent of the conjugative transposons. Therefore we compared the element to the conjugative transposon Tn. The II restriction maps of the two elements differed and no hybridization was detected to oligonucleotides directed to the ends of Tn. However, the elements do have some sequence homology, detected by hybridization analysis.


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