The β-lactamase that is responsible for bacterial resistance to β-lactam antibiotics was expressed more efficiently in a transformant,
Escherichia coli SD 7 (
topA 10, gyrB 225), which harbored the plasmid pUC 18, than in strain JTT 1 (
top+, gyr+), which also harbored pUC 18. This observation together with the
in vitro finding that the promoter activity of the β-lactamase gene is affected by template topology _??_Brahms
et al.: J. Mol. Biol., 181, 455 (1985)_??_ suggests that a topological difference in pUC 18 in different strains of
Escherichia coli can affect gene expression.
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