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