Incorporation of Labelled Precursors into Nucleic Acids of Subcellular Fractions and Polyribosomal Patterns by G. Moruzzi, B. Barbiroli and C. M. Caldarera

1. An increase in polyamine concentration, caused by inhibiting the amine oxidase activities with iproniazid, increased the incorporation of [3H]orotic acid into chick-embryo RNA and DNA. On the other hand, a decrease in polyamine concentration, obtained by causing an increase in amine oxidase activities, decreased [3H]orotic acid incorporation into nucleic acids. This was particularly evident for nuclear DNA and ribosomal RNA. 2. Polyribosomal patterns obtained by sucrosedensity-gradient centrifugation showed highest radioactivity in the regions of 259s and 280s aggregates in those embryos in which the polyamine contents were enhanced, whereas a decrease in the radioactivity was observed when the polyamine concentrations were decreased. 3. The activity of DNA-dependent RNA polymerase, assayed in the same experimental conditions, also varied in the same fashion with changes in polyamine concentration.