Mutations altering chromosomal protein H-NS induce mini-Mu transposition
M Falconi1, V McGovern, C Gualerzi
1Department of Biochemistry, University of Alabama, Birmingham 35294.
Abstract:
Bacteriophage Mu is one of the most efficient transposons known, capable of moving a hundred viral copies to new positions in the bacterial chromosome in an hour. Mu also forms stable lysogens. In bacteria lysogenic for the defective protein fusion-forming phage MudII1681, which can transpose and replicate but does not encode genes for DNA packaging and cell lysis, the frequency of transposition changes as colonies age. To find host genes that alter the spontaneous Mu transposition frequency, we used a genetic screen with mini-MudlacZ fusion formation as an assay. H-NS (also called H1a and B1) is an abundant nonspecific DNA-binding protein localized to the bacterial chromosome. H-NS has an unusual structure of interspersed patches of acidic and basic residues reminiscent of eukaryotic HMG proteins. Mutations in hns caused an increase in Mu-specific transcription and a dramatic increase in MudII1681 transposition rates when cells were put under certain growth conditions. Purified H-NS stabilized Mu repressor-DNA complexes in vitro, suggesting that H-NS contributes to the organization of transcriptionally inactive DNA in vivo.
Insights
Host factor H-NS regulates bacteriophage Mu transposition. Mutations in hns significantly increase MudII1681 transposition rates, indicating H-NS
Area of Science:
- Bacteriology
- Molecular Biology
- Genetics
Background:
- Bacteriophage Mu is a highly efficient transposon, capable of rapid integration into bacterial chromosomes.
- Defective phage MudII1681 can transpose and replicate but lacks genes for packaging and lysis.
- Spontaneous transposition frequency of MudII1681 changes with colony age.
Purpose of the Study:
- To identify host genes influencing spontaneous Mu transposition frequency.
- To investigate the role of H-NS protein in regulating Mu transposition.
Main Methods:
- Utilized a genetic screen employing mini-MudlacZ fusions to assay transposition frequency.
- Investigated the effect of mutations in the hns gene on MudII1681 transposition.
- Examined the in vitro interaction of purified H-NS with Mu repressor-DNA complexes.
Main Results:
- Mutations in the hns gene led to increased Mu-specific transcription.
- A significant increase in MudII1681 transposition rates was observed under specific growth conditions in hns mutants.
- Purified H-NS protein stabilized Mu repressor-DNA complexes in vitro.
Conclusions:
- H-NS (histone-like nucleoid-structuring protein) plays a crucial role in modulating bacteriophage Mu transposition.
- H-NS likely contributes to the organization of transcriptionally silent DNA, thereby repressing Mu transposition.
- Understanding H-NS function provides insights into the regulation of mobile genetic elements in bacteria.
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