Alternatively, the second primer sequence may be based upon {HEAD ~ sequences} derived from {TAIL ~ the cloning vector} 
Alternatively , the second primer sequence may be based upon { HEAD ~ sequences } derived from { TAIL ~ the cloning vector }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL