Promotor locus

Pastan and Perlman [100] investigated the relationship between catabolite repression, cyclic AMP action, and the promotor locus. They studied a promotor mutant (L8) which is insensitive to transient repression on addition of glucose. In this strain, cyclic AMP had no effect. However, revertant strains of L8 have regained their sensitivity to transient repression, and cyclic AMP increased the production of galactosidase, in the presence of glucose, by over 60%. In a different promotor mutant (L29), repression in response to glucose was normal and cyclic AMP displayed its normal ability to overcome repression. 

The studies outlined above indicate that a new model of catabolite repression involving a positive control system is beginning to emerge. This model can be summarized as follows In the presence of glucose or other catabolite repressor, the cellular level of cyclic AMP is reduced. This reduction leads to the inability of the cells to initiate lac messenger RNA synthesis. Cyclic AMP acts at the promotor locus, in conjunction with a protein, believed to be an activator protein for promoting initiation of RNA synthesis. 

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