The intracellular flow and the transfer to progeny phages of the single stranded parental DNA of the filamentous phage MI3 has been studied in Escherichia coli KMBL 42 a t low multiplicities of infection (< I). The cellular bound parental DNA was found to be Grst converted quantitatively into replicative form DNA. Then, contrary to the events in phage @X 174 infection the parental DNA is further transferred as a complete molecule to the pool of single stranded progeny DNA and to progeny phage particles. The efficiency of transfer per infecting phage is approximately as high as 0.75 and 0.5, respectively. Evidence is presented that during transfer the parental DNA is incorporated into DNA strands having up to several times the length of single stranded phage DNA.During the course of the replication of the single stranded DNA phage @XI74 the infecting single strands are converted into double strands, the parental replicative form molecules and are attached as membrane bound replicative form t o special sites in the bacterium [1,2]. From there considerable transfer of the parental strands to daughter replicative form molecules in the cytoplasm and to progeny phage is found only a t rather high multiplicities of infection (> 3) [3]. At low multiplicities depending on the sensitivity of the method involved either no [4,5] or only a very small transfer [6] can be detected. From these results it is concluded that in the case of @XI74 an irreversible binding of the parental strands to a special site is a prerequisite for the further synthesis of daughter replicative form and progeny single strands. To test whether this rule held only for the single stranded DNA phage @Xi74 or whether it is of more general importance, intracellular flow and transfer to progeny of the single stranded parental DNA of the filamenteous phage MI3 was studied a t low multiplicities of infection. Under the conditions used radioactive labelled parental DNA was found to be transferred as intact molecules to the progeny. prove the transfer of intact parental DNA of phage fd which is closely related to phage M13. Furthermore, a standard transfer experiment was designed during which the parental DNA strands of the irreversibly adsorbed phages are transferred quantitatively into the replicative form fraction. Based on this result the specific transfer of parental DNA through replicative form to the pool of ss-progeny DNA and into mature progeny phage was studied quantitatively. Preliminary results on the mechanism of the transfer show that the standard transfer experiment which has been developed may serve as a useful tool t o study replication of single stranded viral DNA.
MATERIALS AND METHODS
Bacteria, Phages and Xtandard MediumAn hcr-strain, Escherichia coli K12 KMBL 42 F', a generous gift of Dr. A. Roersch, Leiden, was, unless otherwise stated, employed as host bacterium for MI3 in all experiments. This strain proved advantageous as all phages which adsorbed to the bacteria in the time allowed, almost quantitatively penetrated and went into ecli...