Naturally occurring R factors are classified into two types, fi
+ and fi
-, depending on their fi characters. The term fi is an abbreviation of fertility inhibition and fi
+ and fi
- mean, respectively, the presence and absence of suppression of the functions of the sex factor F of
Escherichia coli K-12.
It was found that fi
- R factors reduce the efficiency of plating of phage λ in K-12; fi
+ R factors did not have this inhibitory action. We have studied the mechanism of suppression of progeny formation of phage λ by fi
- R factors and have obtained the following results.
1. The adsorption of phage λ was not altered by the presence of any R factors.
2. Transduction of the ability to ferment galactose with λdg was reduced by fi
- R factors in the recipients.
3. The lysogenization with λ was also reduced by the presence of fi
- R factors.
4. Spontaneous production as well as ultraviolet induction of λ was not affected by any R factors.
5. Zygotic induction of prophage λ was not affected by any R factors in the recipients.
6. “Helper effects” of modified normal λ were observed in the transduction of Gal
+ with unmodified λdg into restricting
E. coli carrying fi
- R factors with the exception of R factor N-1.
From these results, it is concluded that suppression of progeny formation of phage λ by fi
- R factors is due to some step after adsorption of the phage to the bacteria. It is further assumed that the nucleic acid of phage λ is broken down following injection.
Furthermore, it was found that phage λ undergoes host-induced modification in the host carrying some fi
- R factors. At least two types of fi
- R factors were recognized by the types of their restriction and host-induced modification of phage λ.
Lastly, CaCl
2 exhibited an antagonistic action against the restriction of phage λ by fi
- R factors; MgCl
2 did not show such an antagonistic action.
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