IS1634, a novel insertion element creating long, variable-length direct repeats which is specific for Mycoplasma mycoides subsp. mycoides small-colony type

A new insertion sequence, IS1634, has been identified in Mycoplasma mycoides subsp. mycoides small-colony type (SC), IS1634 shows structural and functional similarities to IS1549 of Mycobacterium smegmatis and with it seems to form a new class or family of insertion sequences. IS1634 has a size of 1,872 bp, including two 13-bp terminal inverted repeats. It contains an open reading frame (ORF) encoding a product of 533 amino acids which shows similarity to the transposase of IS1549 and to a lesser extent to the transposases of IS elements of the IS4 family, IS1634 is present at about 30 copies in the genome of all 22 different field strains of M. mycoides subsp. mycoides SC tested. Characteristic of IS1634 are the long and variable-length direct repeats at the sites of insertion which were found to reach up to about 500 bp. IS1634 is specific to M. mycoides subsp. mycoides SC and is not present in any of the other members of the M. mycoides cluster. Neither was it found in other closely related Mycoplasma species of ruminants.