Identification of an Insertion-sequence-like Genetic Element in the Newly Recognized Human Pathogen Mycoplasma Incognitus

Cloned 2.2-kb DNA (plasmid psb-2.2) of Mycoplasma incognitus, a pathogen in AIDS and non-AIDS patients [Lo et al., Am. J. Trop. Med. Hyg. 41 (1989) 364-376; 601-616], contains a 1405-bp genetic element closely resembling bacterial insertion sequence (IS) elements. This IS-like element has 29-bp terminal inverted repeats with seven mismatches, is immediately flanked by 3-bp direct repeats, and has typical stem-and-loop structures at or near both the termini. Two potential open reading frames (ORF-1 and ORF-2) encode 143 amino acids (aa) and 103 aa, respectively, in this IS-like element. Part (57 aa) of the deduced aa sequence of ORF-2 has a significant homology (43%) with the putative transposase of Escherichia coli IS3. In this study, a series of synthetic oligodeoxyribonucleotides each containing a specific sequence of a selected segment in psb-2.2, have been used as probes which reveal that the IS-like element occurs more than ten times in the genome of M. incognitus. This potentially transposable element has many characteristic features in common with bacterial IS elements.