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Evidence for a conservative pathway of transposition of bacteriophage Mu
Abstract:
During its lytic cycle bacteriophage Mu uses repeated transposition as a mode of DNA synthesis. These transpositional events are undoubtedly replicative, and presumably semi-conservative. In a Mu lysogen this type of transposition can start immediately after prophage induction. However, in an infective cycle the Mu genome (which is injected into the host cell as a linear molecule flanked by short random sequences of bacterial DNA) must first become integrated into the host chromosome. Little is known about how this occurs apart from the fact that the bacterial sequences at either end of the Mu genome are lost in the process. The integration is thus similar to a transposition event. In an attempt to determine whether this type of Mu transposition (between a linear donor molecule and a circular recipient) is also semi-conservative we have analysed the progeny phage arising from an infective cycle in which the parental DNA was heterozygous for a known genetic marker. The expectation is that if integration of the infecting Mu genome occurs by a single semi-conservative transpositional event then pure phage bursts should be produced as the genetic information on only one strand would be preserved throughout the lytic cycle. The experiments reported here do not support this expectation in that the infected cells yield mixed bursts, suggesting that Mu integration is a conservative, rather than a semi-conservative event.
Insights
Bacteriophage Mu DNA synthesis involves transposition. Experiments show Mu genome integration into host DNA during infection is conservative, not semi-conservative, producing mixed progeny.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- Bacteriophage Mu utilizes replicative transposition for DNA synthesis during its lytic cycle.
- Prophage induction in Mu lysogens initiates transposition immediately.
- Mu genome integration into the host chromosome during infection is poorly understood, involving loss of flanking bacterial DNA.
Purpose of the Study:
- To investigate whether bacteriophage Mu integration into the host chromosome during an infective cycle is a semi-conservative process.
- To determine the mechanism of Mu DNA integration by analyzing progeny phage from heterozygous parental DNA.
Main Methods:
- Analysis of progeny phage from bacteriophage Mu infective cycles.
- Utilizing parental DNA heterozygous for a known genetic marker.
- Comparing experimental results with expectations for semi-conservative vs. conservative integration.
Main Results:
- Infected cells produced mixed phage bursts, not pure bursts as expected for semi-conservative integration.
- The experimental outcomes did not support the hypothesis of a single, semi-conservative transpositional event for Mu integration.
- Findings suggest Mu integration is a conservative event.
Conclusions:
- Bacteriophage Mu integration into the host chromosome during infection appears to be a conservative process.
- This contrasts with the presumed semi-conservative nature of transpositional DNA synthesis during the Mu lytic cycle.
- Further research is needed to fully elucidate the Mu integration mechanism.