{TAIL ~ Methods} of screening for {HEAD ~ nucleoside analogs} that are incorporated by HIV reverse transcriptase and cause incorrect base pairing 
{ TAIL ~ Methods } of screening for { HEAD ~ nucleoside analogs } that are incorporated by HIV reverse transcriptase and cause incorrect base pairing
TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH