What does the Roman numeral following the name of a restriction enzyme indicate?

The order in which the enzyme is isolated from a strain of bacteria.

The correct answer is Option (1) - The order in which the enzyme is isolated from a strain of bacteria.

Restriction enzymes are named after the bacterial species from which they are originally isolated, and the Roman numeral is used to distinguish different enzymes isolated from the same species.

For example, EcoRI is a type of restriction enzyme isolated from Escherichia coli (E. coli), and the Roman numeral I indicates that it was the first enzyme of this type to be discovered from this bacterial strain.

If there were another type of restriction enzyme isolated from the same bacterial strain, it might be named EcoRII or EcoRIII, with the Roman numeral indicating the order of discovery.