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Cloning and characterization of the genes encoding the MspI restriction modification system
P M Lin1, C H Lee, R J Roberts
1Cold Spring Harbor Laboratory, NY 11724.
Abstract:
The genes encoding the MspI restriction modification system, which recognizes the sequence 5' CCGG, have been cloned into pUC9. Selection was based on expression of the cloned methylase gene which renders plasmid DNA insensitive to MspI cleavage in vitro. Initially, an insert of 15 kb was obtained which, upon subcloning, yielded a 3 kb EcoRI to HindIII insert, carrying the genes for both the methylase and the restriction enzyme. This insert has been sequenced. Based upon the sequence, together with appropriate subclones, it is shown that the two genes are transcribed divergently with the methylase gene encoding a polypeptide of 418 amino acids, while the restriction enzyme is composed of 262 amino acids. Comparison of the sequence of the MspI methylase with other cytosine methylases shows a striking degree of similarity. Especially noteworthy is the high degree of similarity with the HhaI and EcoRII methylases.
Insights
Researchers cloned and sequenced the MspI restriction-modification system genes. The MspI methylase gene shows significant similarity to other cytosine methylases, particularly HhaI and EcoRII.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Restriction-modification systems are crucial for DNA protection and gene regulation.
- The MspI system targets the 5' CCGG sequence, involving both restriction and methylation.
- Understanding these systems provides insights into DNA modification and recognition mechanisms.
Purpose of the Study:
- To clone and characterize the genes responsible for the MspI restriction-modification system.
- To determine the genetic organization and sequence of the MspI genes.
- To compare the MspI methylase sequence with other known methylases.
Main Methods:
- Gene cloning into the pUC9 vector.
- Selection based on methylase expression and MspI insensitivity.
- Subcloning and DNA sequencing of the MspI genes.
- Bioinformatic analysis of gene sequences and protein products.
Main Results:
- Successful cloning and subcloning of the MspI methylase and restriction enzyme genes into a 3 kb DNA fragment.
- Determination of divergent transcription of the two genes.
- The MspI methylase gene encodes a 418-amino acid polypeptide; the restriction enzyme gene encodes a 262-amino acid polypeptide.
- High sequence similarity was observed between MspI methylase and other cytosine methylases, notably HhaI and EcoRII.
Conclusions:
- The MspI restriction-modification system genes have been successfully cloned, sequenced, and characterized.
- The MspI methylase shares significant homology with other cytosine methylases, suggesting conserved functional domains.
- This study provides a foundation for further investigation into the structure-function relationships of MspI and related enzymes.