The nomenclature of restriction enzymes uses a three letter in DNA: E. coli, HpaII , MspI

The nomenclature of restriction enzymes uses a three letter
description that indicates the organism from which it has been
identified. The first letter designates the genus and rest two are derived from the first two letters of the species. For example EcoRI
is derived from E. coli, Hind UI is derived from Hacinophilus influeza and so on. To differentiate among restriction enzymes from

different strains of same organism, further letters are used to
denote the strains or in some cases vectors etc. Further, if more
than one R. E. are present in same strain, roman letters are used to
describe them. Therefore Hind III is the third enzyme found in
Hacinopizilus influeza strain Rd. A list of different R. E. is provided
in Table 2 with their recognition sites.

Some R. E. recognizes same base sequence and cut at the recognition site. If these enzymes restrict the sequence at the same site, they are termed as isoschizonzers. HpaII and MspI are two isoschizomers recognizing 5’CCGG3’ sequence. However, some enzymes although recognize same sequence but cut at different regions. Smal and Xnial are two such enzymes and are termed as smal & zmal as both recognize the sequence 5’CCCGGG3’, but Smal produces blunt end while X?nnl produces 5’ overhang with sticky end.