AN APYRIMIDINIC SITE KINKS DNA AND TRIGGERS INCISION BY ENDONUCLEASE-VII OF PHAGE-T4

Apurinic/apyrimidinic lesions (AP-sites) occur frequently ire DNA, gen erated by physically and chemically induced or spontaneous loss of bas es. Repair mechanisms have evolved in organisms to deal efficiently wi th AP-sites by first incising the DNA at the lesion, followed by excis ion and resynthesis of the damaged strand, Here we report that endonuc lease VII (endo VII) of phage T4, which was originally classified as a debranching and Holliday structure resolving enzyme, also recognizes AP-sites with high efficiency. The enzyme cleaves both strands of doub le-stranded DNA in a stepwise fashion a few nucleotides 3' of the lesi on. In a search for a recognition signal shared by all known endo VII substrates, kinking of DNA has earlier been suggested as such a signal , In support of this hypothesis, we demonstrate here that AP-sites ind uce distinct kinks in synthetic oligonucleotides allowing efficient in tramolecular ring closure by ligation.