The polymerase chain reaction may also be performed on {HEAD ~ a library} of cloned nucleic acid fragments wherein the sequence of one primer is derived from {TAIL ~ the instant nucleic acid fragments}, and the sequence of the other primer takes advantage of the presence of the polyadenylic acid tracts to the 3′ end of the mRNA precursor encoding plant genes 
The polymerase chain reaction may also be performed on { HEAD ~ a library } of cloned nucleic acid fragments wherein the sequence of one primer is derived from { TAIL ~ the instant nucleic acid fragments } , and the sequence of the other primer takes advantage of the presence of the polyadenylic acid tracts to the 3′ end of the mRNA precursor encoding plant genes
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH