Sequence relations among the IncY plasmid p15B, P1, and P7 prophages
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Abstract:
Electron microscopic analysis of heteroduplex molecules between the 94-kb plasmid p15B and the 92-kb phage P1 genome revealed nine regions of nonhomology, eight substitutions, and two neighboring insertions. Overall, the homologous segments correspond to 83% of the P1 genome and 81% of p15B. Heteroduplex molecules between p15B and the 99-kb phage P7 genome showed nonhomology in eight of the same nine regions; in addition, two new nonhomologous segments are present and P7 carries a 5-kb insertion representing Tn902. The DNA homology between those two genomes amounts to 79% of P7 DNA and 83% of p15B. Plasmid p15B contains two stem-loop structures. One of them has no equivalent structure on P1 and P7 DNA. The other substitutes the invertible C segments of P1 and P7 and their flanking sequences including cin, the gene for the site-specific recombinase mediating inversion.
Insights
Comparing plasmid p15B with phage P1 and P7 genomes using electron microscopy revealed significant DNA homology and structural differences. These findings highlight genetic variations and rearrangements between these key genetic elements.
Area of Science:
- Molecular Biology
- Genetics
- Microbiology
Background:
- Plasmids and bacteriophages are crucial genetic elements in microbial systems.
- Understanding the genomic relationship between plasmids and phages is essential for molecular biology research.
- Plasmid p15B, phage P1, and phage P7 are significant entities in microbial genetics.
Purpose of the Study:
- To analyze the structural and homologous relationships between plasmid p15B and the genomes of phage P1 and phage P7.
- To identify regions of nonhomology, substitution, and insertion in the heteroduplex molecules.
- To investigate the presence and significance of unique structural features, such as stem-loop structures and invertible segments.
Main Methods:
- Electron microscopic analysis of heteroduplex DNA molecules formed between plasmid p15B and phage P1.
- Electron microscopic analysis of heteroduplex DNA molecules formed between plasmid p15B and phage P7.
- Quantification of homologous and nonhomologous DNA segments.
Main Results:
- Heteroduplex analysis between p15B and P1 revealed 83% homology, with nine nonhomologous regions, eight substitutions, and two insertions.
- Heteroduplex analysis between p15B and P7 showed 83% homology, with eight shared nonhomologous regions, additional nonhomologies, and a 5-kb insertion (Tn902) in P7.
- Plasmid p15B possesses two distinct stem-loop structures, one unique and another substituting invertible segments and the cin recombinase gene found in P1 and P7.
Conclusions:
- Significant genomic homology exists between plasmid p15B and phages P1 and P7, indicating shared ancestry or genetic exchange.
- Specific regions of nonhomology, insertions (like Tn902), and unique structural elements (stem-loops, invertible segments) define the distinct identities of these genetic elements.
- The findings provide insights into the evolutionary dynamics and structural organization of these important microbial genetic entities.