In summary, rII mutations induced by exposure of T4 phage particles to either visible light or proflavine are acridine revertible. In both cases mutation occurs without inactivation. The rII mutations induced by the photodynamic action of proflavine on T4 phage particles are equally divided between the acridine revertible and base analogue revertible classes. It is proposed that photodynamic action induces base analogue mutations and that the acridine revertible category arises from the separate effects of light and proflavine.

From studies involving inhibition of DNA synthesis in Hfr strains of Escherichia coli K12, either by thymine starvation (Pritchard, 1963) or amino-acid starvation (Suit, Matney, Doudney & Billen, 1964), during mating with F− strains, it has been concluded that transfer of DNA from males to females can occur in the absence of DNA synthesis. This conclusion is at variance with the hypothesis (Jacob, Brenner & Cuzin, 1963) that the energy required for transfer is derived from the process of DNA replication. On the other hand, a second prediction from this hypothesis, that one polynucleotide chain of the DNA transferred during mating will have been synthesized during transfer, is strongly supported by recent experiments (Ptashne, 1965; Blinkova, Bresler & Lanzov, 1965; Gross & Caro, 1965).