THE INSERTION-SEQUENCE ELEMENT ISRM2011-2 BELONGS TO THE IS630-TC1 FAMILY OF TRANSPOSABLE ELEMENTS AND IS ABUNDANT IN RHIZOBIUM-MELILOTI

The insertion sequence (IS) element ISRm2011-2 of Rhizobium meliloti ( Rm) is characterized by 19-bp imperfect terminal inverted repeats (thr ee mismatches) and a size of 1053 bp. Upon transposition, ISRm2011-2 g enerates a putative target duplication of 2 bp. ISRm2011-2 carries two major overlapping open reading frames (ORFA and B) with a coding capa city of 135 and 201 amino acids (aa), respectively, A potential transl ational frameshifting window (5'-AAAAAAAG) is located in the overlappi ng region of both ORFs, The putative fusion product of both proteins, which probably represents the mature transposase, has a predicted mole cular mass of 35.8 kDa and a pI of 10.5, Comparison of the deduced aa sequence of ORFA with database entries revealed homology to putative t ransposases of some IS elements of the IS3 family, as well as to eukar yotic transcription factors. The protein encoded by ORFB shows homolog y to transposases (Tps) of the recently proposed IS630-Tc1 family whic h includes Tps of both prokaryotic and eukaryotic transposable element s, Analyses of the distribution of ISRm2011-2 in natural Rm population s showed that this IS element is abundant in Rm strains.