Nature of a polynucleotide required for polyribonucleotide formation from adenosine triphosphate with an enzyme from thymus nuclei.

Two enzymes, each specific for the polymerization of single nucleoside triphosphates into polynucleotides, have been purified from extracts of calf thymus nuclei. The purification and properties of an adenosine triphosphate (ATP) polymerasel have been described (l), and a brief description of the properties of a purified cytidine triphosphate polymerase has appeared (2). The activity of each of these polymerases has been shown to be completely dependent on a polynucleotide which can be isolated from each purified enzyme (3). This report will describe the isolation and purification of a polyribonucleotide primer from the ATP polymerase. Experimental evidence will be presented indicating that its activity depends upon a sequence of adenine nucleotides of as yet undetermined length. The high adenine nucleotide content (87%) of the purified primer, as well as the observed priming activity by a synthetic polyadenylic acid, suggests that the native primer may exist in situ as a polyadenylic acid. Such nucleotide homopolymers are readily synthesized in vitro from nucleoside diphosphates with bacterial polynucleotide phosphorylases. In contrast to ATP polymerase, however, these enzymes from most bacteria (4) lack specificity and would not be expected to catalyze homopolymer synthesis in vivo. A deoxyribonucleic acid-dependent synthesis of polyadenylic acid from ATP in the absence of other nucleoside triphosphates has been reported recently by Chamberlin and Berg to be catalyzed by a partially purified enzyme from Escherichia coli extracts (5).