THE TRANSPOSABLE ELEMENTS RESIDENT ON THE PLASMIDS OF PSEUDOMONAS-PUTIDA STRAIN H, TN5501 AND TN5502, ARE CRYPTIC TRANSPOSONS OF THE TN3 FAMILY

Genes for (methyl)phenol degradation in Pseudomonas putida strain H (p hl genes) are located on the plasmid pPGH1. Adjacent to the phl catabo lic operon we identified a cryptic transposon, Tn5501, of the Tn3 fami ly (class II transposons). The genes encoding the resolvase and the tr ansposase are transcribed in the same direction, as is common for the Tn501 subfamily. The enzymes encoded by Tn5501, however, show only the overall homology characteristic for resorvases/integrases and transpo sases of Tn3-type transposons. Therefore it is likely that Tn5501 is n ot a member of one of the previously defined subfamilies. Inactivation of the conditional lethal sacB gene was used to detect transposition of Tn5501. While screening for transposition events we found another t ransposon integrated into sacB in one of the sucrose-resistant survivo rs. This element, Tn5502, is a composite transposon consisting of Tn55 01 and an additional DNA fragment. It is flanked by inverted repeats i dentical to those of Tn5501 and the additional fragment is separated f rom the Tn5501 portion by an internal repeat (identical to the left te rminal repeat). Transposition of phenol degradation genes could not be detected. Analysis of sequence data revealed that the phl genes are n ot located on a Tn5501-like transposon.