In a two-year effort, researchers at the Medical Research Council’s Laboratory of Molecular Biology in Cambridge read and redesigned the DNA of the bacterium Escherichia coli (E coli), before creating cells with a synthetic version of the altered genome.
The artificial genome holds 4m base pairs, the units of the genetic code spelled out by the letters G, A, T and C.
Printed in full on A4 sheets, it runs to 970 pages, making the genome the largest by far that scientists have ever built.
The DNA coiled up inside a cell holds the instructions it needs to function. When the cell needs more protein to grow, for example, it reads the DNA that encodes the right protein. The DNA letters are read in trios called codons, such as TCG and TCA.
In 2010, US scientists announced the creation of the world’s first organism with a synthetic genome. The bug, Mycoplasma mycoides, has a smaller genome than E coli – about 1m base pairs – and was not radically redesigned.