{HEAD ~ Primers} oriented in the 3′ and 5′ {TAIL ~ directions} can be designed from the instant sequences 
oriented in
{ HEAD ~ Primers } oriented in the 3′ and 5′ { TAIL ~ directions } can be designed from the instant sequences
HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH