FIG. 1.

Structures of class II catabolic transposons and related transposons. See references 1, 7, 12, 16, 23, and 27 to 30 for details. Symbols and abbreviations: solid arrowhead, terminal IR; open arrowhead, IS1256 (21); open arrow, IS26 (23); solid circle, res site; solid half-circle, defective res site; A, tnpA; R, S, and T, genes for cointegrate resolution; nah, nah genes; xyl, xyl genes; M and M1, meta catabolic pathway operon; U, upper catabolic pathway operon; Hg, genes for resistance to mercuric ion; Sm, gene for resistance to Sm; Su, gene for resistance to sulfonamide; Tc, genes for resistance to Tc; Mcp, gene encoding methyl-accepting chemotaxis protein. The arrow above or below each gene or operon indicates the direction of transcription. Tn4651 and Tn4653 are located on pWW0, Tn4655 is located on NAH7, and Tn4656 is located on pWW53-4. The upper pathway operons encode the enzymes for conversion of toluene and xylenes to their respective carboxylic acids in the case of the TOL plasmids and the enzymes for conversion of naphthalene to salicylate in the case of NAH7. The meta pathway operons are involved in conversion of the final upper pathway products to catechol or its methyl derivatives and then to central metabolites. Tn4656 carries only one (M1) of the two meta pathway operons of pWW53. The regulatory genes xylS and xylR located downstream of the xyl meta pathway operon and the regulatory gene nahR located upstream of the nah meta pathway operon are not shown. Previous papers have clarified (i) the interchangeability of the TnpR functions among Tn21, Tn1722, and Tn4653, (ii) the identity of the amino acid sequences of the Tn4653 and Tn1722 resolvases, (iii) the interchangeability of the TnpA functions between Tn1722 and Tn4653, and (iv) the cointegration of Tn4655 by the Tn1722 or Tn4653 transposase (29, 30).