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