The restriction endonucleases of different organisms
vary in their base sequence specificity. Since the sequence
specificity of restriction endonucleases can be determined,
they have become widely used reagents for cutting DNA at
specific sites, to yield manageable lengths of DNA for
detailed study. Similarly, the DNA ligase of E. coli is an
enzyme that rejoins the ‘nicks’ that may from time to time
occur in DNA and also function in DNA replication.
Methods of DNA analysis based on the application of these
enzymes and techniques for gene transfer became the foundation
tools of genetic manipulation and molecular genetics.
For details the reader is referred to standard texts on molecular
biology, bacterial genetics and genetic manipulation.