1. During the first 10 minutes of viral growth following infection of E. coli by phage T2 in broth, a pool of DNA is built up that contains phosphorus later to be incorporated into phage. This pool receives phosphorus from, but does not contain, the bacterial DNA.

2. After 10 minutes, DNA synthesis and phage maturation keep pace in such a way that the amount of precursor DNA increases moderately for a time and then remains constant.

3. The pool so described is defined in terms of the kinetics of transport of phosphorus from its origins in the culture medium, the bacterial DNA, and the DNA of the parental phage, to the viral progeny. The most interesting parameter of this system is the size of the precursor pool, which measures 10–9 to 2 x 10–9 µg. DNA-P (50 to 100 phage particle equivalents) per bacterium.

4. Neither the precursor nor the intracellular phage population exchanges phosphorus with the phosphate in the medium. More interestingly, the phosphorus in mature phage does not exchange with phosphorus in the precursor, showing that maturation is an irreversible process.

5. Maturation is also a remarkably efficient process. About 90 per cent of labeled phosphorus introduced early into the precursor pool is later incorporated into phage.

6. Viral DNA is synthesized at the rate of about 1.5 x 10–10 µg. DNA-P (7 or 8 phage particles) per bacterium per minute. This is somewhat faster than bacterial DNA is formed, but considerably slower than RNA is formed, in uninfected bacteria.

7. The transport of phosphorus from medium to viral precursor DNA takes an average of 8 or 9 minutes, and from precursor to phage an additional 7 or 8 minutes.

8. Metabolically active RNA has been detected in infected bacteria.

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