Control of uracil transport by cyclic AMP in E. coli.

Previous work from this laboratory indicated that the addition of cyclic adenosine 3’,5’-monophosphate (cyclic AMP) to the culture medium decreases the growth rate of E. cob. The cyclic AMP concentration necessary for growth inhibition is the same as that required for the reversal of permanent catabolite repression [ 11. On the other hand, growth inhibition was not observed in mutants defective in the cyclic AMP receptor protein or when the cyclic nucleotide was replaced by other nucleoside-phosphates [2]. The cyclic AMP-promoted inhibition of growth rate could be due to a decrease in the activity of some enzymatic steps required for the metabolization of certain carbon sources or, in turn, to a more general phenomenon involving for example membrane transport, macromolecular synthesis (DNA, RNA or protein), etc. In fact this inhibition varies with the type of carbon source used in the culture medium. However, all the evidence obtained indicates that the absence of cyclic-AMP effect on the growth rate of bacteria cultured in succinate, malate or glycerol as carbon sources is the consequence of the relatively high levels of the nucleotide within the cells [2]. This paper provides evidence indicating that the culture of E. coli in the presence of cyclic AMP leads to an impairment in the transport of uracil.