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Streptomyces genomes: circular genetic maps from the linear chromosomes
Shih-Jie Wang1, Hua-Mei Chang1, Yi-Shing Lin1
1Institute of Genetics, National Yang-Ming University, Shih-Pai, Taipei 112, Taiwan1.
Microbiology (Reading, England)
|October 12, 1999
Summary
Streptomyces chromosomes, unlike bacteriophages, exhibit circular genetic maps due to a bias for even crossovers during recombination, not circular permutation. This finding clarifies bacterial chromosome mapping.
Area of Science:
- Genetics
- Microbiology
- Molecular Biology
Background:
- Streptomyces species possess linear chromosomes, yet genetic mapping reveals circular linkage patterns.
- This contrasts with bacteriophages T2 and T4, which have circularly permuted linear genomes and form concatemers.
- Unlike bacteriophages, Streptomyces lack these specific structural and replication features.
Purpose of the Study:
- To investigate the mechanism behind the circular genetic maps observed in Streptomyces despite their linear chromosomes.
- To test the Stahl & Steinberg hypothesis regarding recombination bias in Streptomyces.
Main Methods:
- Analysis of genetic linkage based on recombination.
- Physical inspection of telomeres in recombinant chromosomes.
- Interspecies conjugation experiments using linear or circular plasmids.
Main Results:
- Demonstrated that a strong bias toward an even number of crossovers during recombination creates apparent circular genetic linkages.
- Observed this phenomenon in recombinant chromosomes after interspecies conjugation.
- Provided physical evidence supporting the Stahl & Steinberg hypothesis.
Conclusions:
- The circularity of Streptomyces genetic maps is attributed to a recombination bias favoring even crossovers, not genome circularity or permutation.
- This bias is likely influenced by chromosome merozygosity and telomere associations involving terminal proteins.
- Establishes a distinct mechanism for genetic mapping in Streptomyces compared to certain bacteriophages.