Wheat germ DNA polymerase A, a gamma-like enzyme, recognized efficiently natural and synthetic RNA templates, resembling a retroviral reverse transcriptase (P. Laquel et al., Biochim Biophys Acta 1048 (1990):139-148). Ammonium-21-tungsto-9-antimoniate (HPA-23), an antiviral drug, inhibited the DNA polymerase A activities, independently of the template primers used, i.e. activated DNA or polyriboadenylic acid oligodeoxythymidylate (poly(rA)-oligo(dT)). The inhibition observed in the poly(rA)-oligo(dT)-directed DNA polymerase A activity occurred in the presence of either Mg2+, or Mn2+ as divalent cation, and also with the 2'-fluoro analogue of poly(rA) as template. HPA-23 was a noncompetitive inhibitor with respect to TTP, activated DNA, poly(rA)-oligo(dT), and poly(dAfl)-oligo(dT). A preincubation study showed a reversible HPA-23 binding to DNA polymerase A, in the presence of poly(rA)-oligo(dT) as the template primer.23510551060