Effects of dibutyryl-cAMP on expression from P gltBDF and a mutant form with altered Crp binding sites. Cells were grown in a MOPS-based defined glucose rich medium with (closed symbols) or without (open symbols) 10 μM dibutyryl-cAMP. All strains were Crp+. A. Expression of the native lac operon (strain W3110). B. Expression of a PgltBDF-lacZ fusion (strain PM2003). C. Expression of a fusion of lacZ to the mutant version of PgltBDF shown in the bottom line of Fig. 5A (strain PM2004).