The incorporation of cytidine 5′-monophosphate and other ribonucleotides by an enzyme preparation from rat-liver microsomes

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Abstract
An enzyme preparation from rat-liver microsomes incorporated all four ribonucleotides from the corresponding triphosphates into ribosomal RNA. The reaction was Mn2+ dependent, but UMP incorporation also occurred in the presence of Mg2+. The incorporation of any one ribonucleotide was inhibited by the presence of the other three ribonucleoside triphosphates and by denatured DNA. The product of the reaction consisted of short chains of homopolymer attached to the primer ribosomal RNA. "Soluble" RNA, synthetic polyribonucleotides, and oligoribonucleotides were also effective primers for CMP incorporation. When phosphodiesterase-treated "soluble" RNA was the primer, CMP was incorporated into positions usually occupied by the normal terminal trinucleotide sequence of intact "soluble" RNA, but the enzyme did not synthesize a specific terminal sequence consisting of a defined number of CMP residues.