Genetic analyses of the interactions of the IS1-encoded proteins with the left end of IS1 and its insertion hotspot.
Insertion sequence IS1 specifies the InsA, delta InsA-B'-InsB and InsA-B'-InsB protein species. These three proteins have the identical alpha-helix-turn-alpha-helix motif that is likely to be responsible for DNA binding. In fact, InsA binds to the ends of IS1, and regulates gene expression and transposition of IS1. delta InsA-B'-InsB and/or InsA-B'-InsB has been thought to possess a transposase-like activity. Here, I examined the actions of these proteins in vivo on the promoter (pinsL) in the left end of IS1. InsA repressed pinsL-driven gene expression, both in cis and in trans. delta InsA-B'-InsB inhibited it efficiently only when pinsL was located near the construct where delta InsA-B'-InsB is expressed. Furthermore, it has been shown that the possible -10 sequence of pinsL is required for delta InsA-B'-InsB to act on, but the -35 sequence where InsA binds specifically, is not. InsA-B'-InsB appeared not to work on a nearby pinsL. The cis-action of delta InsA-B'-InsB is consistent with the previous observation that the IS1 transposase acts preferentially in cis. Interestingly, delta InsA-B'-InsB acted on a nearby P3 promoter in the IS1 insertion hotspot, and on another promoter outside the hotspot. delta InsA-B'-InsB may generally interact with the regions in or around promoters owing to their low DNA helix stability. Note that IS1 transposes preferentially into A + T-rich DNA segments, and that DNA is unwound from the -10 region of a promoter in transcription. The cis-preference of delta InsA-B'-InsB would result in an overall reduction of transposition of IS1 and its defective copy in a cell, allowing stable existence of the element in its bacterial host.
Matsutani
S
S
National Institute of Health Sciences, Setagaya-ku, Tokyo, Japan.
D001483:Base Sequence; D004254:DNA Nucleotidyltransferases / Q000378:metabolism*; D004251:DNA Transposable Elements / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D004274:DNA, Recombinant; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D019077:Helix-Turn-Helix Motifs / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D011993:Recombinant Fusion Proteins; D019895:Transposases
D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D004274:DNA, Recombinant; D004268:DNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D004254:DNA Nucleotidyltransferases; D019895:Transposases