By combining Ce(IV)/EDTA complex and pseudo-complementary peptide nucleic acid (pcPNA), an artificial restriction DNA cutter which hydrolyzes targeted phosphodiester linkages in double-stranded DNA has been developed. The targeted site in the DNA is activated by two strands of pcPNA and selectively hydrolyzed by the Ce(IV) complex. The DNA cutter required for aimed manipulation can be straightforwardly designed and obtained in terms of (i) the sequence of targeted selective scission, (ii) size of DNA substrate, and (iii) magnitude of desired site-specificity. The sitespecificity can be high enough to cut the whole genome of human beings (3 © 10 9 base-pairs) at one predetermined site. Off-target scissions at the sites of analogous sequences hardly take place. With the use of this specificity, targeted gene can be engineered in human cells through homologous recombination. Other potential applications of this cutter, as well as recent attempts to improve its activity and specificity, are also discussed.
Significance of Site-Selective Scission of DNASite-selective scission of DNA is a key step in biotechnology and molecular biology. For a long time, target DNA for our manipulation has been restricted to small DNA such as plasmids which are composed of 30005000 base-pairs (bp). In order to cut them at a desired site, naturally occurring restriction enzymes, which recognize 4-or 6-bp sequence, have been used. The resultant scission fragments are combined with other fragments with the use of another enzyme ligase. With outstanding developments in relevant fields, however, target DNA of our manipulation is gradually shifting from plasmids to genomes which are directly responsible for the memory of genetic information. Unfortunately, the site-specificity of naturally occurring restriction enzymes is too low to manipulate genomes which are by several orders of magnitude larger than plasmids. For example, human genome is composed of 3 © 10 9 bp. If this DNA of enormous size is treated with a restriction enzyme recognizing a 6-bp sequence, the scission occurs at too many sites (statistically, the scission site of this enzyme should appear at every 4 6 (= 4096) bp, and the number of scission sites in this genome should be larger than half million). Precise manipulation is impossible under these conditions. In order to cut genomes selectively at a desired site, we apparently need artificial cutters which recognize a longer sequence. If one should like to cut human genomes at one site and manipulate them precisely, the length of recognition site of the cutter should be at least 16 bp (note that 4 16 > 3 © 10 9). The importance of these artificial DNA cutters having higher and tunable site-specificity has been widely recognized for a long time, and many researchers have devoted efforts to this subject.1 As a result, remarkable progress has already been accomplished, especially in the design of non-protein molecules which selectively bind to target site in doublestranded DNA. Peptide nucleic acids (PNAs) developed by Nielsen 2...