Inhibitory effect of irradiation of DNA with near ultraviolet light in the presence of 8-methoxypsoralen on cleavage by restriction endonucleases.

pBR322 DNA/Restriction endonuclease/8-methoxypsoralen/Black light/Crosslink The pBR322 DNA was irradiated with black light in the presence of 8-methoxypsoralen and digested by various restriction endonucleases including Hin dIII and Rsa I. It was found that for every restriction enzymes examined digestion products specific for pretreated DNA appeared as expected from the inhibition of cleavage presumably due to the formation of corsslinks at the cutting site or within the recognition se quence. Cleavage by Hin dill was affected sensitively by pretreatment of DNA with irradiation in the pres ence of 8-MOP. The results were discussed in terms of stringency of enzymes to the structural changes of DNA and/or of the unique base sequence favorable to form crosslink.