Escherichia coli is a Gram-negative, non-spore-producing, rod-shaped bacterium that ferments lactose and lives in the intestines of many animals.
This bacterium produces a natural antibiotic called colicin. This chemical kills other bacteria by a variety of methods (depending on the type), such as blocking protein synthesis and degrading DNA. Colicins are encoded by a group of naturally-occurring E. coli plasmids such as Col E1.
E. coli has been widely studied by geneticists, who have created special strains for study:
- HB101: This strain is unusually good at taking in introduced foreign DNA and incorporating it into its own genome. It is therefore commonly used as the host organism for growing recombinant DNA vectors.
- C600 : this strain is used in genetics experiments as a host for foreign plasmids that have been cloned.
This bacterium is also interesting because contains many different DNA genes, which make proteins that are essential for DNA replication:
- dnaA gene: a defective gene which produces a defective protein that influences DNA replication in a variety of ways.
- dnaB gene: makes a protein that is involved in the formation of primer polynucleotide chains, which are precursors of DNA replication.
- dnaE gene (polC gene): makes some of the components of the DNA Polymerase III protein, an enzyme which plays an important role in DNA replication.
- dnaF gene (nrdA gene): codes for an enzyme (ribonucleotide reductase) which breaks down ribonucleotides.
- dnaG gene: makes the enzyme primase, an enzyme which helps make primers, which are precursors to DNA replication.
- dnaH gene (dnaZ gene): makes some of the components of the DNA Polymerase III protein, an enzyme which plays an important role in DNA replication.
- dnaJ and dnaK genes: helps the bacteria survive at high temperatures. They also play an important role in the replication of the DNA of bacteriophage lambda.
- dnaQ gene: also makes some of the components of the DNA Polymerase III protein.