Methods in Molecular Biology • 16 Enzymes of Molecular Biology

CHAPTER 2

Deoxyribonuclease

I (EC 3.1.21.1) and II (EC 3.1.22.1)

A. Fred Weir

1. Introduction
   From Chapter 1 on nucleases, we know that the term DNase refers
   to an enzyme that endonucleolytically cleaves DNA molecules. This
   chapter deals with those DNases that preferentially catalyze the hydro-
   lysis of double-stranded DNA (ds DNA) and that have found a use in
   the various techniques employed in molecular biology. The Type II
   restriction endonucleases obviously fall into this category, however
   they are a large subject on their own and therefore are dealt with in a
   separate section of this book. DNases acting preferentially on single-
   stranded DNA (ss DNA) substrates are also dealt with in another sec-
   tion of this chapter.
   Despite the ubiquitous nature of nucleases in living organisms, it is
   perhaps surprising to find that, apart from the Type II restriction endo-
   nucleases, only one ds DNA DNase enzyme is used routinely in mole-
   cular biology. The reasons for this are twofold. First, as outlined in Chapter
   1, it is very difficult to isolate a DNase in a form that is completely free
   of accompanying RNase and exonuclease contamination and indeed
   these activities may be part of the same enzyme molecule. Obviously,
   it would not be desirable to remove DNA from a precious RNA prepa-
   ration with a DNase that has an integral RNase activity. The second
   reason is that the first DNase isolated from tissues, DNase I (or pan-
   creatic DNase), performs all the tasks very well and can be isolated
   readily in a pure form; why use or look for another enzyme? DNase I

From: Methods in Molecular Biology, VoL 16: Enzymes of Molecular Biology

Edited by: M. M. Burrell Copyright ©1993 Humana Press Inc., Totowa, NJ

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