CHARACTERIZATION AND SEQUENCE OF A NOVEL INSERTION-SEQUENCE, IS1162, FROM PSEUDOMONAS-FLUORESCENS

We have determined the nucleotide sequence of IS1162, a new insertion sequence (IS) isolated from Pseudomonas fluorescens (Pf) strain ST. Th is IS element is present in two copies on the pEG plasmid harboured by Pf ST and in a single copy on the chromosome, adjacent to the styrene catabolic genes. IS1162 is 2634 bp in length with 12-bp terminal inve rted repeats (IR), and could encode four proteins (ORFs), two for each strand. One strand, Pro1 (62990 Da), showed a helix-turn-helix motif at the N-terminal region, and Pro2 (25997 Da) was characterized by the presence of the A and B motives of the NTP (ATP/GTP)-binding site. Co mparison of IS1162 of Pf with known IS showed a high homology with IS4 08 of Burkholderia cepacia [Byrne and Lessie, Plasmid 31 (1994) 138-14 7]. Pro1 and Pro2 were found to be homologous to the corresponding ORF s of IS408, IS21 [Reimmann et al,, Mel. Gen. Genet. 215 (1989) 416-424 ], IS232 [Menou et al., J. Bacteriol. 172 (1990) 6689-6696] and IS5376 [Xu et al., Plasmid 29 (1993) 1-9]. IS1162 transposed at low frequenc y and no cointegrates were found among the transposition products. The target duplication sites, variable in length, showed the presence of homologous motives, suggesting a certain degree of specificity of the IS1162 insertion site.