Chips, Clones, and Living Beyond 100: How Far Will the Biosciences Take Us?

B. Cloning genes

We describe a typical cloning procedure, starting with an illustration of how restriction enzymes work in the process.

Restriction enzymes

One of the first restriction enzymes, dubbed EcoR1, was discovered in E. coli and found to cut only within the nucleotide sequence GAATTC (or its mirror image CTTAAG), and specifically between the G and A. The enzyme cuts both DNA strands of the double helix creating small single-stranded fragments at the cut sites that stick out:

Double-stranded DNA before cutting:

XXXXXXXGAATTCXXXXXXX

XXXXXXXCTTAAGXXXXXXX

Double-stranded DNA after cutting with EcoR1:

XXXXXXXG     AATTCXXXXXXX

XXXXXXXCTTAA GXXXXXXX

Note that the Xs in this example can be A, T, C, or G, corresponding to the basic alphabet ...