A messenger RNA from the lactose operon of Escherichia coli that can not direct the production of functional -galactosidase in absence of exogenous adenosine 3',5-cyclic monophosphate.

In a temperature-sensitive mutant of Escherichia coli, beta-galactosidase cannot be induced at the nonpermissive temperature (43 degrees C) without the addition of exogenous 3', 5'-cyclic AMP (cAMP), although the intracellular concentration of this nucleotide is normal. This specific effect of cAMP is probably general in this strain for those operons which are controlled by the cAMP receptor protein and cAMP, but not for other parts of the chromosome. The lac mRNA produced at 43 degrees C in absence of cAMP is transcribed from the correct DNA strand and it directs the synthesis of enzymatically inactive material cross-reacting with beta-galactosidase. Experiments separating transcription from translation by using rifampicin, suggest that cAMP exerts its effect during initiation of transcription or translation of lac mRNA, but does not affect the propagation of either the messenger or of the beta-galactosidase polypeptide chain.