Formation of an inverted repeat junction in the transposition of insertion sequence ISLC3 isolated from Lactobacillus casei

Abstract

An insertion sequence, ISLC3, of 1351 bp has been isolated from Lactobacillus casei. Formation of IS circles containing a 3 bp spacer (complete junction) or deletion of 25 bp at the left inverted repeat (IRL) between the abutted IS ends of the ISLC3 junction region (deleted junction) was also discovered in the lactobacilli and Escherichia coli system studied. We found that the promoter formed by the complete junction P jun was more active than that formed by the 25 bp deleted junction P djun or the indigenous promoter P IRL . The corresponding transcription start sites for both promoter P jun and P IRL as well as P djun were subsequently determined using a primer extension assay. The activity of transposase OrfAB of ISLC3 was also assayed using an in vitro system. It was found that this transposase preferred to cleave a single DNA strand at the IRR over the IRL end in the transposition process, suggesting that attack of one end by the other was oriented from IRR to IRL.

How Do Transposable Elements Activate Expression of Transcriptionally Silent Antibiotic Resistance Genes?

“…An analogous mechanism is employed by other members of the IS 3 family (IS 2 , IS LC3 ) [ 60 , 61 ], as well as other IS families, including IS 21 , IS 30, IS 256, and IS 1111 (elements of this family preferentially transpose into attC sites of integrons) [ 62 , 63 , 64 , 65 ].…”