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A deoxyribonuclease of Diplococcus pneumoniae specific for methylated DNA
Abstract:
A deoxyribonuclease specific for methylated DNA was isolated from Diplococcus pneumoniae. The enzyme, an endonuclease, degrades DNA for Escherichia coli to fragments of average molecular weight about half a million; it forms discrete fragments from phage lambda DNA. Methyl-deficient E. coli DNA is not attacked, neither is DNA from Micrococcus radiodurans, which contains no methylated adenine or cytosine. Nor is DNA from D. pneumoniae or phage T7 attacked. However, DNA from M. radiodurans, D. pneumoniae, and T7 is attacked after methylation with and E. coli extract. Methylated T7 DNA is degraded to discrete fragments. Although the genetic transforming activity of normal DNA from D. pneumoniae is not affected by the enzyme, transforming activity of methylated DNA is destroyed. The enzyme is designated endonuclease R Dpn I. Under certain conditions another enzyme of complementary specificity can be isolated. This enzyme, designated endonuclease R Dpn II, produces a similar pattern of fragments from the DNA of T7 without prior methylation of the DNA. It also degrades normal DNA for D. pneumoniae. It is suggested that this pair of enzymes plays a role in some unknown control process, which would involve a large fraction of the specific base sequences that are methylated in E. coli DNA and are present but not methylated in DNA from other sources.
Insights
Researchers discovered a new enzyme, endonuclease R Dpn I, from Diplococcus pneumoniae that specifically targets and degrades methylated DNA. This enzyme plays a role in DNA modification and has implications for genetic research.
Area of Science:
- Molecular Biology
- Enzymology
- Genetics
Background:
- DNA methylation is a crucial epigenetic modification involved in various biological processes.
- Specific DNA-modifying enzymes play key roles in maintaining genome integrity and regulating gene expression.
- Understanding DNA-modifying enzymes aids in deciphering complex biological pathways.
Purpose of the Study:
- To isolate and characterize a novel deoxyribonuclease from Diplococcus pneumoniae.
- To investigate the specificity and activity of the isolated enzyme towards methylated and unmethylated DNA.
- To explore the potential biological role of this enzyme and its counterpart.
Main Methods:
- Isolation and purification of deoxyribonuclease from Diplococcus pneumoniae.
- Enzymatic assays using various DNA substrates, including methylated and unmethylated DNA from different sources (E. coli, phage lambda, M. radiodurans, D. pneumoniae, phage T7).
- Analysis of DNA degradation products using molecular weight determination and fragment analysis.
- Assessment of the effect of the enzyme on the genetic transforming activity of DNA.
Main Results:
- A deoxyribonuclease, designated endonuclease R Dpn I, was isolated and found to be specific for methylated DNA.
- Endonuclease R Dpn I degrades methylated Escherichia coli DNA and phage lambda DNA into smaller fragments.
- Unmethylated DNA from various sources, including E. coli, D. pneumoniae, and T7, was not degraded by Dpn I, but became susceptible after in vitro methylation.
- The enzyme destroyed the genetic transforming activity of methylated DNA while leaving normal DNA unaffected.
- A complementary enzyme, endonuclease R Dpn II, was also identified.
Conclusions:
- Endonuclease R Dpn I is a novel enzyme that specifically recognizes and cleaves methylated DNA sequences.
- The discovery of Dpn I and Dpn II suggests a potential role for these enzymes in DNA modification control processes.
- These enzymes may be involved in distinguishing between self and non-self DNA based on methylation patterns, potentially in bacterial defense mechanisms or genome regulation.