THE INTERNAL SEQUENCE OF IS1STIMULATES RNA SYNTHESIS FROM THE IS1OWN AND EXOGENOUS PROMOTERS

Abstract

The bacterial IS1 contains the genes insA and B′-insB encoding transposition related-proteins. The expression of these genes is driven by a promoter within the left end of IS1. Using IS1-lacZ constructs in which lacZs were fused in-frame at various sites of IS1 genes, it was found that the presence of the internal region of insA results in about a 100-fold increase in lacZ expression. The lacZ expression of the fusion constructs in which the IS1 own promoter was displaced by an exogenous promoter, was also stimulated by the presence of the IS1 internal region. Similarly, when lacZ was transcriptionally fused to the internal region of IS1, the lacZ expression from an exogenous promoter was stimulated. This result shows that the IS1 internal region acts as a cis-element to stimulate RNA synthesis from the upstream promoter. This was confirmed by Northern blot analyses. Furthermore, the gene which encodes the factor working with the IS1 internal sequence to stimulate transcription, was cloned. The gene was artA in the transfer region of the Escherichia coli F factor. Interestingly, the cis-element for transcription stimulation is found downstream, whereas many such elements are located upstream, of the promoter.