Phi X 174

The phi X 174 (or phi X) bacteriophage was the first organism to have its DNA-based genome sequenced by Fred Sanger and his team in 1977. In 1962, Walter Fiers had already demonstrated the physical, covalently closed circularity of phi X 174 DNA.

This phage has a very small amount of DNA. It has 11 genes in 5386 bases (it is single stranded) in a circular topology. Several of them expressing similar function in two groups. The GC-content is 44% and 95% of nucleotides are coding genes.