A Poly(A) Polymerase from Calf Thymus

A purification procedure for a poly(A) polymerase has been developed for calf thymus tissue which gives a protein without detectable ribonuclease activity. During the purification, a manganese stimulated poly(A) synthesis is removed and poly(A) synthesis becomes dependent on exogenous polyribonucleotides. This same purification procedure applied to calf thymus nuclei gives a poly(A) polymerase activity indistinguishable from that of homogenates of the whole tissue. The most purified polymerase shows one major band after electrophoresis on polyacrylamide gel. A molecular weight of 140,000 to 160,000 has been estimated by gel filtration analysis. The polymerase is highly specific for ATP and is inhibited by other ribonucleoside triphosphates. It is more active in the presence of Mg++ than Mn++ and is inhibited at 0.1 ionic strength. Polymerization of ATP can proceed at linear rates for several hours. Some basic kinetic properties of the reaction have been studied. The reaction is insensitive to high levels of cordycepin, α-amanitin, and actinomycin D.