NAPHTHALENE DEGRADING GENES ON PLASMID NAH7 ARE ON A DEFECTIVE TRANSPOSON

A 37.5 kb region encompassing a set of the naphthalene degrading genes on the Pseudomonas plasmid NAH7 was found to be transposable only in the presence of the transposase encoded by the Tn 1721 subgroup of the class II transposons. This newly identified mobile element, designated Tn 4655, contained short (38 bp) terminal inverted repeats which shared extensive sequence homology with those of members of the Tn 1721 subgroup. Tn 4655 transposed by a two-step process involving formation of the cointegrate followed by its subsequent resolution. In contrast to the defect in the trans-acting factor for the first step, a functional system for the latter step was encoded within a 2.4 kb region in Tn 4655. Analysis of deletion and insertion mutants demonstrated that the 2.4 kb region contained the cis-acting (res) site and the gene for a trans-acting factor (resolvase); complementation analysis indicated that Tn 4655 resolvase function was not interchangeable with those of other well-studied class 11 transposons, including the Tn 1721 subgroup. Tn 4655 had no DNA sequences that were hybridizable with the transposase or resolvase genes of the Tn 1721 subgroup. © 1990 Springer-Verlag.