Enzymes catalysing the non-transcriptive polymerisation of ATP, UTP, GTP and CTP to the corresponding ribohomopolymers have been isolated from rat liver nuclei. By chromatography on agarose and phosphocellulose two different poly(A) polymerases, a Mg++-dependent and a Mn++-dependent poly(A) polymerase, have been resolved. A Mn++-dependent enzyme system synthesizing poly(U), poly (G) and poly(C) from UTP, GTP and CTP is co-purified with the Mn++-dependent poly(A) polymerase. For the synthesis of the ribohomopolymers a primer-RNA, but not DNA, is essential. The polymerases described have a molecular weight of 41,000 daltons; they are not identical with the DNA-dependent RNA polymerase or polynucleotide phosphorylase.
