What does the Roman numeral in a restriction enzyme name indicate?

Correct answer: The order in which the enzyme was isolated from that bacterial strain

The Roman numeral in a restriction enzyme name shows the order in which a restriction enzyme was identified or isolated from the same bacterial strain. For example, in EcoRI, I indicates the first such enzyme identified from that particular strain of Escherichia coli. The bacterial species is indicated by the initial letters of the name, not by the Roman numeral. Exam tip: Remember the I in EcoRI as the first enzyme isolated from that strain.