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Nucleoside triphosphate phosphohydrolase associated with cytoplasmic polyhedrosis virus
Abstract:
Nucleoside triphosphate phosphohydrolase [EC 3.6.1.15] activity was found to be included in silkworm cytoplasmic polyhedrosis (CP) virus, which synthesizes mRNA carrying the 5'-terminal modification. This enzyme releases orthophosphate from the gamma-position in a nucleoside triphosphate, leaving nucleoside diphosphate. The rate of hydrolysis of ATP is faster than that of any other ribonucleoside triphosphate. Deoxy ATP is hydrolyzed rather faster than ATP. However, polynucleotides carrying triphosphate at the 5'-terminus, that is, 4S RNA which was synthesized by E. coli RNA polymerase [EC 2.7.7.6] using calf thymus DNA as a template, and the phage Q beta RNA (30S), are not effective substrates for this enzyme. Although the CP virion loses the viral genome and one kind of protein component on proteolytic treatment with pronase, the partially degraded virion still retains phosphohydrolase activity. The phosphohydrolase must therefore be associated firmly with the virion. This enzyme does not require the presence of nucleic acid for its function. Phosphohydrolysis of ATP by this enzyme activity represents a first step in the synthesis of the 5'-terminal modified mRNA of CP virus.
Insights
Silkworm cytoplasmic polyhedrosis virus contains a nucleoside triphosphate phosphohydrolase. This enzyme is crucial for mRNA 5'-terminal modification, initiating synthesis by hydrolyzing ATP.
Area of Science:
- Virology
- Enzymology
- Molecular Biology
Background:
- Silkworm cytoplasmic polyhedrosis virus (CPV) synthesizes mRNA with a 5'-terminal modification.
- The mechanism and enzymatic basis for this modification were not fully understood.
Purpose of the Study:
- To identify and characterize the enzyme responsible for the initial step in 5'-terminal mRNA modification in CPV.
- To investigate the properties and substrate specificity of this enzyme.
Main Methods:
- Enzyme assays using various nucleoside triphosphates and polynucleotides.
- Proteolytic treatment of CP virions to assess enzyme association.
Main Results:
- CP virus contains nucleoside triphosphate phosphohydrolase activity (EC 3.6.1.15).
- The enzyme preferentially hydrolyzes ATP and deoxy ATP, releasing orthophosphate.
- The phosphohydrolase activity is retained in partially degraded CP virions, indicating firm association.
- The enzyme functions independently of nucleic acid presence.
Conclusions:
- The identified phosphohydrolase is integral to the CP virion and essential for mRNA 5'-terminal modification.
- ATP hydrolysis by this enzyme is the first step in CP virus mRNA capping.