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