Introduction

Cloning and manipulating genes requires the ability to cut, modify and join genetic material (usually DNA, but sometimes RNA) and check the parameters of the molecules, such as size, that are being manipulated. We will assume knowledge of the structure of the materials involved (DNA, RNA and so on) and start by describing the tools available for manipulating them. Many of the tools involved are enzymes that have important physiological roles in cells. To understand why they are useful for our purposes, we should be aware of their normal roles, too.

The choice of which enzyme is used for a particular purpose depends mainly on two considerations:

1. How easy (i.e. inexpensive) is it to purify? This will be determined by its abundance in the cell and by how easy it is to separate it from other undesirable activities.

2. How well does it do the job? This will depend upon its specificity (‘accuracy’) and specific activity (‘speed’) and upon the details of the reaction which it catalyses.

Other factors, such as stability, are also important.

Techniques of genetic manipulation can be applied to the production of the enzymes for genetic manipulation itself. It is possible to use cloned genes to prepare large quantities of these enzymes more easily, as well as to modify the genes to ‘improve’ their function, perhaps by slightly altering the properties of the enzymes they encode.