Conventionally in naming restriction enzymes, the first word of the name is taken from the genus and the second and third word taken from the species of the former nucleotides from which they were isolated e.g. Eco R1, Eschocichia Coli Ry 13, the letter (R) in Eco R1 is taken from the name of the strain. The roman numerals after the name inticate the order in which the enzymes were first.