Abstract
Low concentrations of urea specifically inhibit the expression of catabolite sensitive genes (the lactose, galactose and maltose operons and the tryptophanase gene). This inhibition depends upon growth conditions, i.e. carbon source and temperature. The main effect of urea is exerted at the level of transcription initiation. However an additional inhibitory effect is observed on the decay and expression of the beta-galactosidase messenger. In a strain harboring the UV5 mutation in the lactose promoter, the effect at the level of transcription is relieved while the effect on the decay and the expression of the beta-galactosidase messenger remains the same. Just like the extreme physiological catabolite repression, the urea effect occurs even in a cya delta strain and is not antagonized by addition of adenosine 3'-5' cyclic monophosphate.
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