RESUMO
We have previously demonstrated the presence of topoisomerase I (topo I) activity in purified retroviral particles (i.e., human immunodeficiency virus type 1, equine infectious anemia virus-EIAV and moloney murine leukemia virus). In our present work, an attempt was made to determine the nature and origin of the protein that is associated with this activity. For that purpose we have isolated the topo I activity from equine infectious anemia virus cores and showed that a major protein band of an 11 kDa is present in the topo I active fractions. It was able to form a DNA-protein cleavable complex, which is one of the characteristics of topoisomerases. This protein was recognized by anti-EIAV p11 nucleocapsid protein (NC) antibodies that can also specifically remove the topo I activity from the purified topo I active fractions. Therefore, our present findings, which are compatible with our previous data concerning the HIV NC protein, suggest that the 11 kDa protein which is associated with the topo I activity in EIAV is the nucleocapsid protein.
