ato Operon: a Highly Inducible System for Acetoacetate and Butyrate Degradation in Escherichia coli

Abstract

Growth of Escherichia coli in the presence of acetoacetate as inducer stimulates the rate of synthesis of two enzymes, an acetoacetyl‐CoA: acetate CoA‐transferase and a thiolase by a factor of 3000. The combined action of these enzymes allows for the degradation of acetoacetate to acetate and acetyl‐CoA. The structural genes for these enzymes, called ato A (CoA‐transferase) and atoB (thiolase), and a regulatory gene, atoC, are closely linked, forming an operon (ato operon) with the order his…atoCAB…nalA on the bacterial chromosome. The regulatory gene atoC is defined by a spontaneous mutation to the atoCc state which allows E. coli to grow on butyrate and to synthesize the enzymes of the ato operon constitutively. This mutation can only be selected for when the enzymes of the C‐3 oxidation pathway are themselves formed constitutively. The atoCc state is required for butyrate degradation because this acid does not serve as inducer of the ato operon but requires the CoA‐transferase for activation. The evidence so far available indicates that the atoCc mutation is trans‐ dominant over the inducible atoC+ state suggesting a positive mechanism of control. The uptake of butyrate is reduced or completely suppressed when mutational lesions prevent the further metabolism of this substrate. Copyright © 1972, Wiley Blackwell. All rights reserved