R因子とλフアージの関係

Abstract

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, CaCl2 exhibited an antagonistic action against the restriction of phage λ by fi- R factors; MgCl2 did not show such an antagonistic action.