Incorporation of nucleoside triphosphates into ribonucleic acid with a particulate fraction of disrupted thymus nuclei

Abstract

A DNA-containing particulate fraction which catalyzes the incorporation of nucleoside triphosphates into RNA has been isolated from homogenates of calf-thymus nuclei. The 5'-triphosphates of adenosine, guanosine, uridine and cytidine were all required for optimal activity, and all four were incorporated. Pretreatment with DNAase or partial removal of DNA with strepomycin resulted in inhibition of the in corporation reaction. Partial reactivation was obtained by adding back calf-thymus DNA. Despite a contaminating nuclease, evidence was obtained that the newly formed RNA reflected the composition of thymus deoxyribonucleic acid. During incubation, a part of both the endogenous and the newly formed RNA was convverted to a non-sedimentable form. Despite a gross similarity in the two fractions, experiments with ³²P-labeled cytidine and ATP indicated an increase in the non-sedimentable fraction of the dinucleotide sequences, guanylyl-(3',5')-cytidine and guanylyl-(3',5')-adenosine, at the expense of the cytidylyl-(3',5')-cytidine and adenylyl-(3', 5')-adenosine sequences.