Retroviruses are widely prevalent among vertebrates and are the causative agents of a variety of diseases in humans and animals including immunodeficiences, leukemias, and lymphomas (1 ). The retrovirus family is characterized by the presence of virion-associated reverse transcriptase (RT), an enzyme that transcribes the viral genomic RNA into a double-stranded DNA copy. This feature has led to studies of the unique enzymatic function of RT for two main applications. First, RT is a good diagnostic tool for the generic detection of the presence of retroviruses. Second, the RT enzyme constitutes a primary target for antiviral drug therapy (1 ,2 ).