isolating {HEAD ~ the polypeptide} from {TAIL ~ the culture} to obtain a polypeptide 17; and 
isolating { HEAD ~ the polypeptide } from { TAIL ~ the culture } to obtain a polypeptide 17 ; and
OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH