Isoschizomers are pairs of

restriction enzyme A restriction enzyme, restriction endonuclease, REase, ENase or'' restrictase '' is an enzyme that cleaves DNA into fragments at or near specific recognition sites within molecules known as restriction sites. Restriction enzymes are one class o ...

s specific to the same

recognition sequence A recognition sequence is a DNA sequence to which a structural motif of a DNA-binding domain exhibits binding specificity. Recognition sequences are palindromes. The transcription factor Sp1 for example, binds the sequences 5'-(G/T)GGGCGG(G/A)(G/ ...

. For example, SphI (CGTAC/G) and BbuI (CGTAC/G) are isoschizomers of each other. The first

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

discovered which recognizes a given sequence is known as the

prototype A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and Software prototyping, software programming. A prototyp ...

; all subsequently identified enzymes that recognize that sequence are isoschizomers. Isoschizomers are isolated from different strains of

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

and therefore may require different reaction conditions. In some cases, only one out of a pair of isoschizomers can recognize both the

methylated In the chemical sciences, methylation denotes the addition of a methyl group on a substrate, or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation, with a methyl group replacing a hydrogen atom. These t ...

as well as unmethylated forms of

restriction sites Restriction sites, or restriction recognition sites, are located on a DNA molecule containing specific (4-8 base pairs in length) sequences of nucleotides, which are recognized by restriction enzymes. These are generally palindromic sequences (beca ...

. In contrast, the other restriction enzyme can recognize only the unmethylated form of the restriction site. This property of some isoschizomers allows identification of methylation state of the restriction site while isolating it from a

bacterial strain In biology, a strain is a genetic variant, a subtype or a culture within a biological species. Strains are often seen as inherently artificial concepts, characterized by a specific intent for genetic isolation. This is most easily observed in mic ...

. For example, the restriction enzymes

HpaII HpaII (IntEnz: EC 3.1.21.4') is a restriction enzyme obtained from the microorganism ''Haemophilus parainfluenzae''. It is a DNA restriction enzyme, therefore it has the ability to cut the DNA from certain region as demonstrated below. It has th ...

and MspI are isoschizomers, as they both recognize the sequence 5'-CCGG-3' when it is unmethylated. But when the second C of the sequence is methylated, only MspI can recognize it while HpaII cannot. An enzyme that recognizes the same sequence but cuts it differently is a

neoschizomer Neoschizomers are restriction enzymes that recognize the same nucleotide sequence as their prototype but cleave at a different site. In some special applications this is a very helpful feature. For example:Prototype MaeII A^CGT produces DNA frag ...

. Neoschizomers are a specific type (subset) of isoschizomer. 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 Isocaudomers are pairs of restriction enzymes that have slightly different recognition sequences, but upon cleavage of DNA, generate identical overhanging termini sequences. These sequences can be ligated to one another, but then form an asymme ...

References

See also