Bulletin Spring‧Summer 1995

Restriction Enzymes: The Key to DNA Mystery DNA Likened to the Book of Life 'The book of life' is how the DNA molecule is often referred to, and this analogy makes it possible to understand why the DNA is one of the prime targets of research in modem biology. To elucidate the analogy, the 'book' consists of long sequences, or 'sentences', with individual genes, or 'words', which are in turn made of base pairs A, T, G, C, which are the basic 'alphabets'! If we could but read the 'book' in detail, the secret of life would be revealed, and many of life's processes could be controlled. Recombinant DNA Research In recombinant DNA research, DNA fragments from different origins can be joined; the genes on these fragments can then be located, and analysed. By turning on the genes, large amounts of useful proteins can be made. Recombinant DNA research can thus be likened to the 'find', 'cut' and 'paste' functions in a word processor. But, we need to know what agent or tool is available to cut the long DNA sequences into defined pieces, before specific genes can be identified by other means. Studies show that it is the restriction enzymes that could do the job, i.e. they are the scissors in DNA research. Restriction Enzymes What are restriction enzymes? They are bacterial enzymes that can not only recognize, but also cleave specific DNA sequences. The cleaved DNA hence have defined ends and can be joined on to another DNA fragment having similar ends. The repertoire of restriction enzymes, as it exists, can only recognize about 200 specific cleavage sites, and many DNA sequences are not covered by this. The current technology is hence much like an incomplete word processor that can only recognize a limited number of sites on the sentences. So, what happens to the unrecognized sites? And, to make matters even more difficult, some of these restriction enzymes are rather rare, and not commercially available. Research 24