Polyamine enhancement of the synthesis of adenylate cyclase at the translational level and the consequential stimulation of the synthesis of the RNA polymerase σ28 subunit

The effects of polyamines on the synthesis of various a subunits of RNA polymerase were studied using Western blot analysis. Synthesis of sigma (28) was stimulated 4.0-fold and that of sigma (38) was stimulated 2.3-fold by polyamines, whereas synthesis of other a subunits was not influenced by polyamines. Stimulation of sigma (28) synthesis was due to an increase in the level of cAMP, which occurred through polyamine stimulation of the synthesis of adenylate cyclase at the level of translation. Polyamines were found to increase the translation of adenylate cyclase mRNA by facilitating the UUG codon-dependent initiation. Analysis of RNA secondary structure suggests that exposure of the Shine-Dalgarno sequence of mRNA is a prerequisite for polyamine stimulation of the UUG codon-dependent initiation.