Research Article 16: Mutants Missing a Factor Necessary for the Expression of Catabolite-Sensitive Operons in E. coli

The lac † operon of E. coli is subject to at least two types of control. First, the well-known negative control in this system involves the action of a specific repressor protein which interacts with the lac operator to inhibit transcription of the lac operon (Jacob and Monod, 1961; Gilbert and Muller-Hill, 1967). A second control mechanism consists of effects variously known as catabolite repression, transient repression or the glucose effect. In simple terms, it can be shown that the lac operon, and all other operons or genes which are inducible and determine the ability of E. coli to use various compounds as carbon and nitrogen sources are partially or nearly totally repressed in glucose minimal media. Until recently the mechanism of the glucose effect was obscure. However, within the last two years, evidence has accumulated both as to the nature of the effector (small molecule catabolite) and the site of action within the lac operon of the glucose effect. Following studies on 3′5′ cyclic AMP in E. coli by Makman and Sutherland (1965), it was shown by Perlman and Pastan (1968) and Ullmann and Monod (1968) that the glucose effect could be completely reversed by addition of 3′5′ cyclic AMP to growth media. Further, Silverstone and co-workers (Silverstone, Magasanik, Reznikoff, Miller, and Beckwith, 1969; Silverstone, Arditti, and Magasanik, 1970) and Perlman, deCrombrugghe, and Pastan (1969) have shown that mutants of the lac promoter site render the lac operon insensitive to glucose effects. These findings have allowed the formulation of various...