Synthèse du poly U par la RNA polymérase avec l’acide octoadénylique (hepta adénylyl-(3′,5′)-adénosine) comme matrice

Abstract

The octoadenylic acid (Ap)₇A serves as a template for poly U synthesis by Escherichia coli RNA polymerase. Two types of polymerisation reaction can be observed by varying the divalent cation concentration in the reaction mixture. High clivaient cation concentrations (4−6 × 10⁻³ M MnC1₂) permit a limited poly U synthesis which stops when the quantity of UTP polymerised corresponds to approximately 2 moles per mole of template A. When reaction is carried out at 27° polymerisation stops completely after the plateau level of 2 U/A is reached but at 37° it continues slowly beyond this point. Addition of template to an incubation mixture in which poly U synthesis has stopped causes reaction to start again, and to continue to a new plateau corresponding to polymerisation of 2 moles of UTP per mole of additional template A. These results show that at high divalent cation concentrations poly U synthesis stops because the template is consumed, probably by its immobilisation in a complex of the type poly A — 2 poly U. In media containing low concentrations of divalent cations (10⁻³ M MnCl₂) poly U synthesis is not limited by the amount of template used. Under these conditions the template functions catalytically. A biphasic incorporation curve is observed with a small reduction in the reaction rate at a point corresponding to the polymerisation of 2–3 moles of UTP per mole of template A. Beyond this point reaction continues at a linear rate for long periods and incorporations of up to 20 moles of UTP per mole of template A have been observed.