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Gene Cloning and DNA Analysis: An Introduction, Sixth Edition ...

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Chapter 11 Studying <strong>Gene</strong> Expression <strong>and</strong> Function 203<br />

Figure 11.23<br />

(a) The oligonucleotide<br />

(b) Complementary str<strong>and</strong> synthesis<br />

(c) Isolation of phage carrying the mutation<br />

Phage carrying<br />

the normal gene<br />

<strong>Gene</strong> in M13 vector<br />

Plaques<br />

Oligonucleotide<br />

Plate onto<br />

agar<br />

One method for oligonucleotide-directed mutagenesis.<br />

gly ala asn leu met<br />

GGA GCT AAT TTA ATG<br />

CCT CGA ATA AAT TAC<br />

gly ala tyr leu met<br />

Non-complementary mismatch<br />

<strong>DNA</strong> polymerase<br />

dNTPs<br />

Plaque<br />

hybridization<br />

Probe with labelled<br />

oligonucleotide<br />

Normal gene<br />

sequence<br />

Oligonucleotide<br />

Entire complementary<br />

str<strong>and</strong> is synthesized<br />

Phage carrying<br />

the mutated gene<br />

Plaques containing<br />

the mutated gene<br />

Using an oligonucleotide to create a point mutation in a cloned gene<br />

There are a number of different ways of carrying out oligonucleotide-directed mutagenesis;<br />

we will consider one of the simplest of these methods. The gene to be mutated<br />

must be obtained in a single-str<strong>and</strong>ed form <strong>and</strong> so is generally cloned into an M13<br />

vector. The single-str<strong>and</strong>ed <strong>DNA</strong> is purified <strong>and</strong> the region to be mutated identified by<br />

<strong>DNA</strong> sequencing. A short oligonucleotide is then synthesized, complementary to the<br />

relevant region, but containing the desired nucleotide alteration (Figure 11.23a). Despite<br />

this mismatch the oligonucleotide will anneal to the single-str<strong>and</strong>ed <strong>DNA</strong> <strong>and</strong> act as a<br />

primer for complementary str<strong>and</strong> synthesis by a <strong>DNA</strong> polymerase (Figure 11.23b). This

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