We have identified a newly discovered virus-coded enzyme termed p32pol in avian retroviruses. This protein possesses a molecular weight of 32,000 on SDS-polyacrylamide gels and is encoded by the polymerase gene of avian retroviruses. We have established this fact by peptide mapping and immunological studies. AMV or RSV p32pol possess a DNA endonuclease activity which prefers supercoiled DNA's as substrates. Various protein-DNA interaction studies are presently underway. We have also demonstrated a new enzyme activity, a Mg ions and Mn ions dependent DNA endonuclease activity, associated with avian retrovirus alpha Beta DNA ploymerase, but not with alpha DNA polymerase. The parent molecule of p32pol, Beta, apparently is responsible for this newly discovered activity. We are concentrating our efforts on understanding the function of this enzymatic activity associated with the avian reverse transcriptase.