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