The photochemical DNA computing via 5-carboxyvinyl-deoxyuridine (U-cv) in anchor oligodeoxynucleotides (ODNs) in order to tether the multiple "DNA words" was demonstrated. A new MARK and UNMARK operation based on the cvU mediated reversible DNA photoligation has been developed for multiple-words DNA computing. The utility of this operation for DNA computing was demonstrated by solving a satisfiability problem (SAT problem) in which information was encoded in three tandem words.