Cleaving Genes - Restriction Enzymes

Before we consider an artificial restriction enzyme, we will briefly explain the mechanism by which ribonuclease A hydrolyzes RNA (Fig. 6.12). In the 

Actual RNA has been cleaved by the artificial enzyme shown in Fig. 6.14 which is a mimic of Staphylococcal nuclease. This is molecular-cleft-type artificial enzyme, where guanidinium residues connected to a rigid backbone 

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Cleaving Genes - Restriction Enzymes Restriction enzymes can cleave nucleic acids at specific sequences. Artificial restriction enzymes can be prepared by combining oligo(nucleic acids) and supramolecular catalytic sites. 

Another use of polytene chromosomes is microdissection of DNA for cloning (Fig. 26-14). A piece of DNA containing 100-400 kb can be cut out of any desired spot, cleaved with restriction enzymes, and cloned.282 Since it has been estimated that Drosophila may contain only -9000-17,000 genes there may be 2-3 genes per band in these chromosomes.283 The technique has been extended to human and other mammalian chromosomes.284... 

Figure 12.10 Some genes and restriction sites on the E. coli plasma pBR322. Eco RI, Pst I, and Sal I are restriction endonucleases and the sites cleaved by these enzymes.

Variations may occur in restriction sites so that, for example, a sequence within a gene may be cleaved by a specific restriction enzyme but its allele may not. 

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