Integrase

The name given to the key enzyme in retroviral integration has evolved through several stages over the past 15 years, reflecting incremental progress in our understanding of its role and activities. This enzyme was initially identified by its apparent molecular weight (e.g., p32 for RSV or ALV, p46 for MLV), then labeled “endonuclease,” in recognition of the protein's weak and relatively nonspecific endonuclease activity observed in assays using unnatural DNA substrates; then “integration protein,” when genetic evidence had established that it was essential for integration, but the specific part it played was not yet clear; and finally “integrase,” when it became clear that it was the enzyme that actually catalyzed the key chemical steps in integration. “Integrase,” sometimes abbreviated as IN, is now generally accepted, and because it appropriately represents the protein's in vivo function and in vitro activities, it is not likely to be superseded.