ThepyrGgene fromLactococcus lactisencodes CTP syn-thase (EC ), an enzyme converting UTP to CTP. A series of strains were constructed with different levels of pyrGexpression by insertion of synthetic constitutive pro-moters with different strengths in front strains expressed pyrGlevels in a range from 3 to 665% relative to thewild-type expression the level of CTP synthase to 43% had no effect on the growth rate, showing that the capacity of CTP synthase in the cell is in excess in a wild-type strain. .
