In another embodiment, the method comprises: testing the mutagenic potential of a nucleoside analog, determining extension by HIV RT of the analog, and comparing {HEAD ~ incorporation} by {TAIL ~ HIV RT} of the analog with incorporation by mammalian DNA polymerase, therefrom determining whether the analog is incorporated preferentially by HIV RT 
In another embodiment , the method comprises : testing the mutagenic potential of a nucleoside analog , determining extension by HIV RT of the analog , and comparing { HEAD ~ incorporation } by { TAIL ~ HIV RT } of the analog with incorporation by mammalian DNA polymerase , therefrom determining whether the analog is incorporated preferentially by HIV RT
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