ISRF1, A TRANSPOSABLE INSERTION-SEQUENCE FROM SINORHIZOBIUM-FREDII

Sinorhizobium fredii strain HH103, a nitrogen-fixing bacterial symbion t of plants, contains an insertion sequence (IS) that can transpose in to plasmid pMUS248 and activate a promoterless TCR gene that is normal ly not expressed. We have cloned and characterized this element, which we designate ISRf1. The IS is 1002 bp in length, contains a single 51 3-bp open reading frame (ORF), is flanked by imperfect 36-bp terminal inverted repeats, and creates 5-bp target duplications. Two copies of ISRf1 are present in the genome of HH103, but it is absent from 12 oth er Sinorhizobium and Rhizobium strains. The element transposes at a fr equency of 2.7 x 10(-6) per generation per cell. (C) 1997 Elsevier Sci ence B.V.