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Chromosomal recombination in Haemophilus influenzae
Abstract:
Haemophilus influenzae cultures doubly lysogenic for defective phage HP1, with a prophage marker sequence +b+/a+c, always contained some free wild-type phage. Single ultraviolet-irradiated cells produced either no wild-type phage or large numbers of them. This suggested that the phage was not released by the original double lysogen but by internal recombinants, i.e., by double lysogens with altered prophage marker sequence such as +++/abc or +b+/++c. Thirty-one wild-type phage-producing clones have been isolated independently from cultures of this double lysogen and identified. They fell in five classes. Two classes, still possessing all three prophage markers, can be explained by Campbell's (1963) prophage recombination model. The other classes had lost one or more markers. They can be explained by interchromosomal double-strand DNA breakage and rejoining. A single-DNA-strand gene conversion model is discussed in view of the fact that genetic transformation involves single-DNA-strand exchanges. A number of potentially interesting mutants has been analyzed of which only the derivatives of rec1 mutant DB117 (obtained from Dr. J. Setlow) were incapable of internal recombination.
Insights
Internal recombination in Haemophilus influenzae double lysogens produces wild-type phage. This process involves altered prophage marker sequences, suggesting DNA breakage and rejoining mechanisms are key to phage release.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Haemophilus influenzae cultures doubly lysogenic for defective phage HP1 exhibit spontaneous wild-type phage production.
- This phenomenon suggests internal recombination events within the prophage DNA.
Purpose of the Study:
- To investigate the mechanisms underlying wild-type phage production in double lysogens.
- To characterize the genetic alterations associated with phage release.
Main Methods:
- Isolation and characterization of wild-type phage-producing clones from double lysogenic cultures.
- Analysis of prophage marker sequences in resulting clones.
- Comparison of observed recombination patterns with existing models.
Main Results:
- Thirty-one wild-type phage-producing clones were identified, falling into five classes.
- Two classes were explained by Campbell's prophage recombination model.
- Other classes showed loss of prophage markers, consistent with interchromosomal double-strand DNA breakage and rejoining.
Conclusions:
- Wild-type phage production arises from internal recombinants with altered prophage marker sequences.
- Both Campbell's model and DNA breakage/rejoining mechanisms contribute to recombination.
- A single-DNA-strand gene conversion model is proposed, and rec1 mutant derivatives were incapable of internal recombination.