Characterization of ISPsy2 and ISPsy3, Newly Identified Insertion Sequences in Pseudomonas syringae pv. eriobotryae

Two new active insertion sequences, ISPsy2 and ISPsy3, were isolated from Pseudomonas syringae pv. eriobotryae, the causal agent of stem cankers of loquat trees. ISPsy2 is 1194-bp long, has 16-bp imperfect terminal inverted repeats, and generates a 4-bp target site duplication upon insertion into the selective cartridge of the entrap vector pSHI1063. The nucleotide sequence of ISPsy2 is completely identical with that of the previously identified IS-like element located adjacent to the virulence gene psvA of Pseudomonas syringae pv. eriobotryae NAE6. The single open reading frame of ISPsy2 encodes a 323-amino-acid protein that has similarity to the transposase of the IS5 subgroup of the IS5 family. The ISPsy3 belonging to the IS91 family is 1507 bp in length, does not duplicate its target sequence, GAAC, and presents an 81% sequence homology with IS801 in P. s. pv. phaseolicola. The transposase of ISPsy3 possesses the conserved amino acid motifs found in the rolling-circle replication protein. Southern blot analysis indicated that multiple copies of ISPsy2 and ISPsy3 are present in the genomes of P. s. pv. eriobotryae and some of the other P. s. pathovars tested. Received 16 August 2001/ Accepted in revised form 19 October 2001