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The host specificity system in Escherichia coli SK
Molecular and Cellular Biochemistry
|November 30, 1976
Summary
E. coli SK possesses a unique DNA host specificity enzyme system. This system involves a methylase that modifies DNA and a virus-specific enzyme that degrades S-adenosylmethionine (SAM) during phage infection.
Area of Science:
- Molecular Biology
- Microbiology
- Enzymology
Background:
- Escherichia coli (E. coli) strains exhibit distinct DNA host specificity systems.
- E. coli SK's enzyme system for DNA specificity differs from known E. coli K12 and E. coli B types.
- Phage transfer experiments between E. coli SK and other strains reveal modification and restriction patterns.
Purpose of the Study:
- To investigate the DNA host specificity mechanism in E. coli SK.
- To isolate and characterize the methylase responsible for DNA modification.
- To understand the role of viral infection on the host's enzyme systems.
Main Methods:
- Isolation and partial purification of a methylase from E. coli SK.
- In vitro enzymatic assays using S-adenosylmethionine (SAM) and DNA.
- Analysis of enzyme activity in E. coli SK cells during phage SD infection, with and without chloramphenicol.
Main Results:
- A methylase was isolated that transfers methyl groups from SAM to DNA, producing 5'-methylcytosine (5'MC) and 6'-methylaminopurine (6'MAP).
- Methylase activity is higher in stationary phase cells compared to logarithmic phase cells.
- Infected E. coli SK cells synthesize a novel enzyme that degrades SAM, preventing in vitro DNA methylation; this enzyme is likely virus-specific and appears early in infection.
Conclusions:
- E. coli SK has a distinct DNA modification system involving a specific methylase.
- Phage SD infection induces a virus-specific SAM-degrading enzyme that inhibits DNA methylation.
- This SAM-degrading enzyme likely acts as a mechanism to prevent host DNA methylation during viral replication.