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Specificity and functions of guanine methylase of Shigella sonnei DDVI phage
Abstract:
DNA methylase methylating adenine with formation of 6-methylaminopurine has been identified in Shigella sonnei 1188 cells which are the natural host of DDVI phage. At the same time, in DNA of DDVI phage replicating both in Sh. sonnei 1188 cells and in Escherichia coli B cells 7-methylguanine was found as the only minor base in amounts of 0.25 and 0.27 mol per 100 mol of nucleotides, respectively. The extract of the infected cells was found to contain both kinds of DNA methylases: virus-specific guanine methylase and cellular adenine methylase. The lack of 6-methylaminopurine in DNA of this phage is explained by reversible inhibition of the cell enzyme in the infected cells. The amount of methyl groups transferred by DDVI-specific methylase on DNA does not depend on the species of the infected cells and is similar in the case of unmodified SD phage DNA and DNA of T2 phage methylated by E. coli B enzyme. Guanine methylase has been shown to be a DDVI-induced modification enzyme and to protect against restriction of B-type. It methylates double-stranded DNAs only and is inhibited by S-adenosylhomocysteine.
Insights
Shigella sonnei DDVI phage induces a guanine methylase that modifies phage DNA, protecting it from restriction enzymes. This virus-specific enzyme functions independently of host cell type.
Area of Science:
- Microbiology
- Molecular Biology
- Virology
Background:
- Shigella sonnei 1188 harbors DDVI phage, a natural host-phage relationship.
- Bacterial DNA methylases play crucial roles in DNA modification and host defense.
Purpose of the Study:
- To identify and characterize DNA methylases involved in DDVI phage replication.
- To understand the mechanism of phage DNA modification and its protective role.
Main Methods:
- Enzyme assays to detect DNA methylase activity.
- Analysis of phage DNA composition using chromatography and nucleotide analysis.
- Investigating enzyme inhibition and substrate specificity.
Main Results:
- A DNA adenine methylase was identified in Shigella sonnei.
- A DDVI-induced guanine methylase was discovered, methylating phage DNA to 7-methylguanine.
- The guanine methylase protects phage DNA from restriction enzymes and methylates double-stranded DNA.
- Cellular adenine methylase activity was reversibly inhibited in infected cells, preventing 6-methylaminopurine formation.
Conclusions:
- DDVI phage encodes a guanine methylase for DNA modification and protection.
- Host adenine methylase activity is suppressed, indicating a sophisticated viral strategy.
- The guanine methylase is a virus-specific modification enzyme protecting against restriction.