Poly(A) polymerase from Vigna unguiculata seedlings. A bifunctional enzyme responsible for both poly(A)-polymerizing and poly(A)-hydrolyzing activities.

Poly(A)-specific ribonuclease was co-purified with poly(A) polymerase from Vigna unguiculata seedlings. Both activities were separated into two forms (enzymes I and II) by a final hydrophobic column chromatography. The enzyme I preparation, which was homogeneous as examined by SDS/PAGE, had both poly(A) polymerase and poly(A)-specific ribonuclease activities. The antibody raised to the enzyme I preparation precipitated both enzyme activities. These indicate that a single polypeptide (Mr 63,000) is responsible for both poly(A)-polymerizing and poly(A)-hydrolyzing activities. The poly(A)-specific ribonuclease was a 3'-exonuclease specific to single-stranded poly(A), forming 5'AMP as the sole reaction product. The hydrolytic activity required either Mn2+ or Mg2+ with different optimum concentrations, whereas the polymerizing activity required Mn2+ but not Mg2+. ATP and PPi had little or no effect on the poly(A)-specific ribonuclease activity.