{HEAD ~ Plasmids} containing {TAIL ~ foreign nucleic acid}, are available commercially, or may be created using conventional methods 
containing
{ HEAD ~ Plasmids } containing { TAIL ~ foreign nucleic acid } , are available commercially , or may be created using conventional methods
HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH