comparing incorporation by HIV RT of {HEAD ~ said analog} with {TAIL ~ incorporation} by a mammalian DNA polymerase, therefrom determining whether said analog is incorporated preferentially by HIV RT 
with
comparing incorporation by HIV RT of { HEAD ~ said analog } with { TAIL ~ incorporation } by a mammalian DNA polymerase , therefrom determining whether said analog is incorporated preferentially by HIV RT
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH