Researchers Clone Bacterial Genes by Splicing DNA with Ligase Enzyme

Collins and colleagues, publishing in Proceedings of the National Academy of Sciences in 1976, describe a method for assembling hybrid, or "chimeric," plasmids by combining DNA from a bacterial plasmid called ColE1 with fragments of the E. coli genome. This is a molecular biology and genetic engineering study, carried out with bacterial cells and enzymes in the lab, not with animals or humans.

The team cut ColE1 DNA and E. coli DNA with a bacterial cutting enzyme, restriction endonuclease EcoRI, then rejoined the fragments using T4 polynucleotide ligase, an enzyme that seals DNA strands together end to end. This let them rebuild two specific genes, one for using galactose and one for using tryptophan, inside new plasmids, even when they started from a mixed, unsorted batch of E. coli DNA rather than pre-sorted gene fragments. After putting these plasmids into bacteria that lacked the genes, they recovered 10 to 20 colonies carrying the desired gene for every microgram of joined DNA used.

The paper reports only this laboratory cloning result. It says nothing about health effects, disease or therapeutic use, and the authors describe their approach as a simple, general method for isolating genes from bacterial DNA rather than a study of any biological effect.