{HEAD ~ PTGS} depends upon transcription of {TAIL ~ the initiating transgene} to function and so if this gets reduced the PTGS will begin to fail 
{ HEAD ~ PTGS } depends upon transcription of { TAIL ~ the initiating transgene } to function and so if this gets reduced the PTGS will begin to fail
HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH