DIVERSITY AND RELATIVE STRENGTH OF TANDEM PROMOTERS FOR THE ANTIBIOTIC-RESISTANCE GENES OF SEVERAL INTEGRONS

The integron is a new type of mobile element containing one or more an tibiotic-resistance-encoding genes site-specifically integrated as cas settes. The integrated genes are expressed from a common promoter regi on located in an adjacent conserved segment. Sequence analysis has rev ealed the existence of four versions of the integron promoters. In thi s study, we have determined the relative strength of the different int egron promoters and compared their activity with that of the tac promo ter. Each version of the promoter was cloned upstream from a promoter- less chloramphenicol acetyltransferase-encoding gene (cat) in plasmid pKK232-8. CAT activity was used to measure transcriptional expression from the promoters of the antibiotic-resistance operon. The strongest promoter is the Version (TTGACAN(17)TAAACT) found in plasmid R388 and in transposon Tn1696. This promoter is six times more efficient than t he derepressed tac promoter.