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

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Chapter 8 How to Obtain a Clone of a Specific <strong>Gene</strong> 135<br />

(a) <strong>An</strong> unstable hybrid<br />

(b) A stable hybrid<br />

(c) A <strong>DNA</strong>–RNA hybrid<br />

Figure 8.9<br />

Short non-complementary regions<br />

do not affect overall stability<br />

<strong>DNA</strong> is bound by the<br />

sugar–phosphate backbone<br />

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

RNA<br />

(a) Transfer colonies to nitrocellulose or nylon<br />

Nitrocellulose/nylon<br />

membrane<br />

(b) Degrade cells, purify <strong>DNA</strong><br />

Bacteria<br />

(c) Probe with labelled <strong>DNA</strong><br />

Alkali +<br />

protease<br />

(d) The resulting autoradiograph<br />

Unpaired bases<br />

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

* * * * * * * Wash * * * *<br />

Non-specific<br />

binding<br />

*<br />

Specific<br />

binding<br />

Figure 8.8<br />

Nucleic acid hybridization. (a) <strong>An</strong> unstable hybrid<br />

molecule formed between two non-homologous<br />

<strong>DNA</strong> str<strong>and</strong>s. (b) A stable hybrid formed between<br />

two complementary str<strong>and</strong>s. (c) A <strong>DNA</strong>–RNA<br />

hybrid, such as may be formed between a gene<br />

<strong>and</strong> its transcript.<br />

Bacteria attached<br />

to the membrane<br />

80°C for 2 hours<br />

or ultraviolet irradiation<br />

Apply<br />

X-ray<br />

film<br />

Positive<br />

hybridization<br />

<strong>DNA</strong> bound<br />

to the membrane<br />

X-ray film<br />

Colony hybridization probing. In this example, the probe is labelled with a radioactive marker <strong>and</strong> hybridization detected<br />

by autoradiography, but other types of label <strong>and</strong> detection system can also be used.

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