Type II restriction enzymes are named after the bacterium from which they have been isolated. The first letter of the genus becomes the first letter of the name of enzyme which is written in capital letter. The first two letters of species make second and third letters of the name of enzyme, which are written in small letters. All the first three letters are written in italics. The fourth letter of the name of enzyme is the first letter of bacterial strain, so written in capital. The Roman number written at the end of the name indicates the order in which the enzyme was isolated from that strain of the prokaryotic cell. For example, the enzyme Eco R I, isolated from the bacterium Escherichia coli RY 13.