Fig. 7.

β-Galactosidase production supported by wild-type and mutant plasmids containing synthetic DAL5 fragments covering positions −398 to −307. The synthesized DNA fragments were cloned into heterologous expression vector pNG15. pJD165, pNG42 and pJD183 contain native DAL5 sequences, whereas their derivatives contain the substitution mutations shown with lower-case letters. The transformation recipient was strain TCY1 which was grown in minimal proline (PRO) or glutamate (GLU) medium prior to assay for β-galactosidase. Figures in parentheses are the quotient of the proline values divided by the glutamate values to yield fold repression.