FIG. 4.

Propionyl-CoA is a required precursor for the signal that triggers prpBCDE expression. β-Galactosidase specific activity is expressed in units per A₆₅₀ unit. The unit of activity for this enzyme is defined in Materials and Methods. The genes listed are ack (encodes acetate kinase), pta (encodes phosphotransacetylase), prpE (encodes propionyl-CoA synthetase), and acs (encodes acetyl-CoA synthetase). All mutations used were insertion alleles which are described in Table 1.