CHARACTERIZATION, NUCLEOTIDE-SEQUENCE, AND CONSERVED GENOMIC LOCATIONS OF INSERTION-SEQUENCE ISRM5 IN RHIZOBIUM-MELILOTI

A target for ISRm3 transposition in Rhizobium meliloti IZ450 is anothe r insertion sequence element, named ISRm5, ISRm5 is 1,340 bp in length and possesses terminal inverted repeats of unequal lengths (27 and 28 bp) and contain five mismatches. An open reading frame that spans 89% of the length of one DNA strand encodes a putative transposase with s ignificant similarity to the putative transposases of 11 insertion seq uence elements from diverse bacterial species, including ISRm3 from R. meliloti, Multiple copies and variants of ISRm5 occur in the R. melil oti genome, often in close association with ISRm3. Five ISRm5 copies i n two strains were studied, and each was found to be located between 8 -bp direct repeats. At two of these loci, which were shown to be highl y conserved in R. meliloti, the copies of ISRm5 were found to be assoc iated with pairs of short inverted repeats resembling transcription te rminators. This structural arrangement not only may provide a conserve d niche for ISRm5 but also may be a preferred target for transposition .