{HEAD ~ Variants} of {TAIL ~ thymidine kinase}, nucleic acids encoding them, and methods of using them 
of
{ HEAD ~ Variants } of { TAIL ~ thymidine kinase } , nucleic acids encoding them , and methods of using them
HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH