Discrepancies between our mapping data concerning the cdd and gat marker of Escherichia coli and data obtained by Josephsen et al. (1983) as well as with the current linkage map of Escherichia coli (Bachmann 1983) led us to reinvestigate the mapping of markers in the gyrA-his region by P1 transduction. In addition, we isolated Hfr strains by integrating the temperature-sensitive F'ts114 lac+ episome via lac homology of cir'lacZ and mgl'lacZ fusions into the chromosome. From the results of the P1 transductions and using these Hfr strains as donors in crosses it became clear that the transcription of cir and mgl is the same and counterclockwise on the chromosome, with cdd and gat as the counterclockwise markers to mgl and cir. We conclude that our previously published sequence of markers was incorrect and is in fact inverted. The present data indicate the following sequence of markers in clockwise order: his gat cdd mgl cir fpk gyrA.
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