5-Iodouracil is a halogenated pyrimidine that can be used in nucleoprotein photo-crosslinking via RNA substitution. 5-Iodouracil is used in thymidine phosphorylase targeted imaging and therapy. Studies show that DNA N-glycosylase MED1 exhibited higher preference for 5-Iodouracil and halogenated bases over non-halogenated ones.