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Microbial genetics has revealed that genes consist of
DNA, an observation that laid the foundation for
molecular biology. Subsequent investigations of bacteria revealed the presence of restriction enzymes that
cleave DNA at specific sites, giving rise to DNA restriction fragments. Plasmids were identified as small
genetic elements capable of independent replication in
bacteria and yeasts. The introduction of a DNA restriction fragment into a plasmid allows the fragment to be
amplified many times. Amplification of specific regions
of DNA also can be achieved with bacterial enzymes
using the polymerase chain reaction (PCR) or other
enzyme-based methods of nucleic acid amplification (eg,
transcription-mediated amplification). DNA inserted
into plasmids within such regions can be placed under
control of high-expression bacterial promoters that
allow encoded proteins to be expressed at high levels.
Thus, bacterial genetics fostered development of genetic engineering, a technology that has been responsible for
tremendous advances in the field of medicine.
