Isoschizomer

Isoschizomers are pairs of restriction enzymes specific to the same recognition sequence.^[1] The term is derived from Greek iso 'same' and skihzo 'to split'.^[2][3]

The first enzyme discovered which recognizes a given sequence is known as the prototype; all subsequently identified enzymes that recognize that sequence are isoschizomers.^[4] For example, the prototype SphI (CGTAC/G) has the isoschizomers BbuI (CGTAC/G) and PaeI.^[5]

In some cases, only one out of a pair of isoschizomers can recognize both the methylated and unmethylated forms of restriction sites, whereas the other enzyme recognizes only the unmethylated form.^[6] This property of isoschizomers allows for the identification of methylation states. For example, the isoschizomers HpaII and MspI both recognize the sequence 5'-CCGG-3' when it is unmethylated.^[7] However, when the second C of the sequence is methylated, only MspI can recognize it.

An enzyme that recognizes the same sequence but cuts it in a different position is a neoschizomer.^[1][4] Neoschizomers are a subset of isoschizomers. For example, SmaI (CCC/GGG) and XmaI (C/CCGGG) are neoschizomers of each other. Similarly KpnI (GGTAC/C) and Acc65I (G/GTACC) are neoschizomers of each other. An enzyme that recognizes a slightly different sequence, but produces the same ends is an isocaudomer.^[8]