Electron microscopy of polar insertions in the lac operon of Escherichia coli |
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Authors: | M. H. Malamy M. Fiandt W. Szybalski |
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Affiliation: | (1) Department of Molecular Biology and Microbiology, Tufts University Boston, Massachusetts;(2) McArdle Laboratory, University of Wisconsin, Madison, Wisconsin |
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Abstract: | Summary Several strongly polar mutations in the omega region of the z gene of the lac operon result from insertions consisting of only two specific sequences of DNA, one about 870 and the other 1170 nucleotide pairs long (based on single-strand measurements). No sequence homology was detected between the shorter (IS1) and longer (IS3) insertions. The IS1 insertion was shown to possess a specific attachment site, but it can be inserted with either orientation at several sites in the z gene. Four insertion sites in the omega region of gene z were identified and the position of the lac5 substitution and the SR2 deletion in the plac DNA were determined by heteroduplex mapping. |
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