Mutant having activity uracil phosphoribosyl transferase.

The present invention relates to a polypeptide having an activity uracil phosphoribosyl transferase (UPRTase) derived from a native UPRTase by mutating one or more residues of said UPRTase. The invention also relates to a nucleotide sequence encoding this mutant UPRTase, a vector for expression of the latter, a viral particle and a host cell and a composition comprising them. Finally it also relates to therapeutic use and to a method of treatment which implements them. The present invention is particularly useful in the context of suicide gene therapy for a particular application with respect to proliferative and infectious diseases.