Conversely, the nucleic acid region may serve to facilitate {HEAD ~ a covalent interaction} between the attached functional unit and {TAIL ~ a given target} 
Conversely , the nucleic acid region may serve to facilitate { HEAD ~ a covalent interaction } between the attached functional unit and { TAIL ~ a given target }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL