Thus, {HEAD ~ the sequence} may be in {TAIL ~ a cell free solution} or placed in a different cellular environment 
Thus , { HEAD ~ the sequence } may be in { TAIL ~ a cell free solution } or placed in a different cellular environment
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH