{HEAD ~ The nucleic acid region} of {TAIL ~ the nucleic acid ligand} serve in whole or in part as ligands to a given target 
{ HEAD ~ The nucleic acid region } of { TAIL ~ the nucleic acid ligand } serve in whole or in part as ligands to a given target
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH