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The T4 mot protein functions as part of a pre-replicative DNA-protein complex
Abstract:
Middle-mode RNA synthesis in T4-infected cells takes place before replication of phage DNA commences. What distinguishes it from early-mode RNA synthesis is that initiation of middle RNA depends on T4-coded proteins, in particular on the mot gene product. mot protein is localized in a DNA-protein complex which forms during the first few minutes of infection. All of the cell's mot protein is bound in this complex, and it continues to be bound long after the synthesis of mot protein has stopped. When we infect Escherichia coli with T4 carrying a temperature-sensitive mutation in the mot gene, we find a correlation between the physiology of this mot mutant and the amount of mot protein bound in the DNA-protein complex. Although there is some host RNA polymerase in the complex, mot protein does not seem to bind to this enzyme. Two other T4-coded proteins, of molecular weights 17,600 and 15,000, are also found in the pre-replicative DNA-protein complex. One of these, p17,600, is coded for by a 750-base pair region located between genes 39 and 56; p17,600 appears to be the recently described motB gene product. The other protein, p15,000, is not an RNA polymerase-binding protein; it is characterized by its strong binding to the DNA-protein complex.
Insights
Middle-mode RNA synthesis in T4 phage requires specific T4-coded proteins, including the mot gene product, which binds to a DNA-protein complex before phage DNA replication begins.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- Middle-mode RNA synthesis in T4-infected cells is distinct from early-mode synthesis.
- Initiation of middle RNA synthesis is dependent on T4-coded proteins, notably the mot gene product.
Purpose of the Study:
- To investigate the role and localization of the mot gene product in T4 phage infection.
- To identify other T4-coded proteins involved in the pre-replicative DNA-protein complex.
Main Methods:
- Infection of Escherichia coli with T4 phage, including strains with temperature-sensitive mutations in the mot gene.
- Analysis of DNA-protein complexes formed during infection.
- Identification of T4-coded proteins within these complexes using molecular weight and genetic mapping.
Main Results:
- The mot gene product localizes to a DNA-protein complex formed early in infection and remains bound.
- A correlation exists between mot mutant physiology and the amount of mot protein in the complex.
- Two additional T4-coded proteins, p17,600 (motB gene product) and p15,000, are identified in the complex; p15,000 exhibits strong DNA-binding properties.
Conclusions:
- The mot gene product and other T4-coded proteins are essential components of a pre-replicative DNA-protein complex that regulates middle-mode RNA synthesis.
- The motB gene product (p17,600) and a novel DNA-binding protein (p15,000) play significant roles in this complex.