Polyamine enhancement of the synthesis of adenylate cyclase at the translational level and the consequential stimulation of the synthesis of the RNA polymerase sigma(28) subunit

The effects of polyamines on the synthesis of various a subunits of RNA pol ymerase were studied using Western blot analysis. Synthesis of sigma (28) w as stimulated 4.0-fold and that of sigma (38) was stimulated 2.3-fold by po lyamines, whereas synthesis of other a subunits was not influenced by polya mines. Stimulation of sigma (28) synthesis was due to an increase in the le vel 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 th at exposure of the Shine-Dalgarno sequence of mRNA is a prerequisite for po lyamine stimulation of the UUG codon-dependent initiation.