The key difference between isoschizomers and neoschizomers is that isoschizomers are restriction enzymes that have the same recognition sequence and cleave the DNA at the same positions, while neoschizomers are restriction enzymes that have the same recognition sequence but cleave DNA at different positions.
Restriction enzymes or restriction endonucleases are enzymes that cleave DNA into fragments at or near specific recognition sites. They cut DNA at restriction sites. Restriction enzymes are usually classified into five groups based on structure, whether they cut their DNA substrate at their recognition site, and whether the recognition and cleavage sites are separate from one another. More than 3600 restriction endonucleases have already been identified. Approximately 800 restriction enzymes are available commercially. Isoschizomers and neoschizomers are two types of restriction enzymes based on recognition site and cleavage specificity.
CONTENTS
1. Overview and Key Difference
2. What are Isoschizomers
3. What are Neoschizomers
4. Similarities – Isoschizomers and Neoschizomers
5. Isoschizomers vs Neoschizomers in Tabular Form
6. Summary – Isoschizomers vs Neoschizomers
What are Isoschizomers?
Isoschizomers are restriction enzymes that have the same recognition sequence and cleave the DNA at the same positions. These restriction enzymes have the same specificity. The first discovered restriction enzyme that recognizes a given sequence is known as a prototype, while all subsequently identified restriction enzymes that recognize that same sequence are called isoschizomers. However, isoschizomers may differ in site preferences, reaction conditions, methylation sensitivity, and star activity. Isoschizomers are isolated from different strains of bacteria. Therefore, they may require different reaction conditions. In some instances, only one out of a pair of isoschizomers can recognize both methylated and unmethylated forms of restriction sites. On the other hand, the other restriction enzyme can recognize only the unmethylated form of the restriction site. This particular feature of isoschizomers helps identification of methylation state of the restriction site while isolating it from a bacterial state.
For example, AgeI and BshT1 recognize and cleave 5’-A↓CCGGT in the same pattern. HpaII and MSPI are other pairs of isoschizomers. They both recognize sequence 5’-C↓CGG-3’ when it is unmethylated. But when the second C of the sequence is methylated, only MSPI can recognize this sequence while HpaII cannot recognize it.
What are Neoschizomers?
Neoschizomers are restriction enzymes that have the same recognition sequence but cleave DNA at different positions. In some special molecular biological applications, this is a very helpful feature. The neoschizomers are a subset of isoschizomers. Well-known examples for neoschizomers are SmaI (5’-CCC↓GGG-3’) and XmaI (5’-C↓CCGGG-3’); both recognize 5’-CCCGGG-3’ sequence but cleave them at a different position. Thus, these two restriction enzymes generate different types of ends. In this case, SmaI produces blunt ends, and XmaI produces 5’ protruding ends.
Figure 01: Neoschizomers
Another example is MaeII and Tail restriction enzymes pair. Prototype MaeII (A↓CGT) produces DNA fragments with a 2-base 5’extension, and neoschizomer Tail (ACGT↓) produces DNA fragments with a 4-base3’ extension.
What are the Similarities Between Isoschizomers and Neoschizomers?
- Isoschizomers and neoschizomers are two types of restriction enzymes.
- They are predominantly found in prokaryotes.
- They are a part of the restriction-modification (RM) system found in bacteria and archaea.
- Both are protein molecules.
- Both cleave DNA into fragments.
What is the Difference Between Isoschizomers and Neoschizomers?
Isoschizomers are restriction enzymes that have the same recognition sequence and cleave the DNA at the same positions, while neoschizomers are restriction enzymes that have the same recognition sequence but cleave DNA at different positions. So, this is the key difference between isoschizomers and neoschizomers. Furthermore, isoschizomers have the same specificities while neoschizomers have different specificities.
The following infographic lists the differences between isoschizomers and neoschizomers in tabular form for side by side comparison.
Summary – Isoschizomers vs Neoschizomers
Restriction enzymes are DNA cutting enzymes. They are also called molecular scissors. There are different types of restriction enzymes. Based on the recognition site and the cleavage specificity, restriction enzymes are two types as isoschizomers and neoschizomers. Isoschizomers have the same recognition sequence and cleave the DNA at the same positions while neoschizomers have the same recognition sequence but cleave DNA at different positions. Thus, this is the key difference between isoschizomers and neoschizomers.
Reference:
1. “Isoschizomer.” An Overview | ScienceDirect Topics.
2. “Restriction Enzymes: Types & Examples.” StudiousGuy, 4 Sept. 2018.
Image Courtesy:
1. “TaiIMae” By Inks002 at the English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia