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Deletion analysis of the cloned replication origin region from bacteriophage M13
Abstract:
A cloned 270-nucleotide fragment from the origin region of the M13 duplex replicative form DNA confers an M13-dependent replication mechanism upon the plasmid vector pBR322. This M13 insert permits M13 helper-dependent replication of the hybrid plasmid in polA cells which are unable to replicate the pBR322 replicon alone. Using in vitro techniques, we have constructed several plasmids containing deletions in the M13 DNa insert. The endpoints of these deletions have been determined by DNA sequence analysis and correlated with the transformation and replication properties of each plasmid. Characterization of these deletion plasmids allows the following conclusions. (i) The initiation site for M13 viral strand replication is required for helper-dependent propagation of the chimeric plasmid. (ii) A DNA sequence in the M13 insert, localized between 89 and 129 nucleotides from the viral strand initiation site, is necessary for efficient transformation of polA cells. A chimeric plasmid containing the viral strand initiation site, but lacking this additional 40 nucleotide M13 sequence, transforms helper-infected cells at a frequency approximately 10(4)-fold less than that of plasmids containing this additional DNA segment. (iii) The entire M13 complementary strand origin can be deleted without affecting M13-dependent transformation by the hybrid plasmids. We propose a model in which replication of one strand of duplex chimera initiates by nicking at the gene II protein nicking site in the viral strand of the M13 insert, followed by asymmetric single-strand synthesis. Initiation of the complementary strand possibly occurs within plasmid sequences.
Insights
Researchers identified key DNA sequences in M13 bacteriophage that enable M13-dependent plasmid replication in bacteria. A specific region is crucial for efficient transformation, revealing insights into viral DNA replication mechanisms.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- The M13 bacteriophage utilizes a specific replication mechanism dependent on its origin of replication.
- The plasmid vector pBR322 requires functional replication machinery for propagation.
- Certain bacterial mutants, such as polA cells, exhibit defects in DNA replication.
Purpose of the Study:
- To investigate the M13 DNA sequences responsible for conferring M13-dependent replication to a plasmid vector.
- To identify the minimal DNA elements required for M13 helper-dependent replication and transformation of polA cells.
- To elucidate the role of specific M13 DNA regions in the initiation and propagation of chimeric plasmids.
Main Methods:
- Cloning of a 270-nucleotide fragment from the M13 origin region into the pBR322 plasmid vector.
- Construction of deletion mutants within the M13 DNA insert using in vitro techniques.
- DNA sequence analysis to determine deletion endpoints.
- Transformation assays and replication studies in M13 helper-infected polA cells.
Main Results:
- A hybrid plasmid containing the M13 insert replicated dependently on M13 helper in polA cells.
- The M13 viral strand initiation site was essential for helper-dependent propagation.
- A 40-nucleotide sequence (nucleotides 89-129 from the viral strand initiation site) was critical for efficient transformation of polA cells.
- Deletion of the entire M13 complementary strand origin did not affect M13-dependent transformation.
Conclusions:
- The M13 origin fragment confers M13-dependent replication and transformation capabilities to pBR322.
- Specific M13 DNA sequences, including the viral strand initiation site and an adjacent region, are crucial for chimeric plasmid propagation and transformation.
- A model is proposed where replication initiates via nicking at the gene II protein site, followed by asymmetric synthesis, with complementary strand initiation potentially occurring within plasmid sequences.