{HEAD ~ Any extensive incorporation} of the labeled nucleotide depends on {TAIL ~ incorporation} and extension of the analog by HIV RT 
depends on
{ HEAD ~ Any extensive incorporation } of the labeled nucleotide depends on { TAIL ~ incorporation } and extension of the analog by HIV RT
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH