Section 3 — Molecular and Microbial Genetics 



to be dissociated from the chromosomes after 

 mitosis. We assume that the acquisition of 

 competence at mitosis for DNA replication 

 may result from a dissociation between the 

 DNA double helix and a previously stabilizing 

 (prenucleolar?) protein. 



1. Unpublished results of R. C. von Borstel, 

 D. M. Prescott, and F. J. Bollum; Bollum, 

 personal communication. 



2. Unpublished result of E. Guttes and F. J. 

 Bollum. 



3. In collaboration with R. A. Ellis, Brown 

 University, R. I. 



3.10. Incorporation of H 3 Thymidine by K12 (A) 

 Induced by Streptonigrin. Charles M. Radding 

 (Michigan, U.S.A.). 



K12(A) is induced by streptonigrin (SN), an an- 

 tibiotic and anti-tumor agent^ 1 )- Like Mitomycin 

 C, SN initiated a rapid breakdown in vivo of the 

 DNA of E. coli to acid soluble products: 35 

 per cent of H 3 labelled DNA was rendered acid 

 soluble in 2 hr. Vegetative multiplication of 

 phage was also initiated, and, in spite of the 

 rapid degredation of the bulk of cellular DNA, 

 all cells could be induced to produce about 

 50 phage per cell. 



The net incorporation of H 3 thymidine (in a 

 1 min pulse) into acid insoluble material was 

 90 per cent inhibited in 20 min by SN in lysogenic 

 and non-lysogenic cells. Only in lysogenic cells 

 was a recovery observed in the ability to incor- 

 porate H 3 thymidine. The peak of this recovery 

 coincided approximately with the appearance 

 of mature intracellular phage. Consistent 

 with incorporation of H 3 thymidine into DNA, 

 both before and after treatment with SN, was 

 the sensitivity of the acid insoluble radioactivity 

 to heating in acid, and stability to heating in 

 alkali. Further studies will attempt to determine 

 if the incorporation of H 3 thymidine by lysogenic 

 cells induced by SN is equivalent to the specific 

 synthesis of A DNA. Preliminary study of 

 defective A lysogens indicates that they are 

 separable into those which can or cannot in- 

 corporate H 3 thymidine after treatment with 

 SN. 



3.1 1. Replication of T2 DNA. F. R. Frankel and 

 L. Ingraham (New York, U.S.A.). 



Bacterial cells infected with bacteriophage T2 

 contain phage particles and intermediate DNA 

 structures. Chloramphenicol (CM) arrests the 

 production of phage but permits continued 

 synthesis of DNA. On removal of the inhibitor, 

 most of the accumulated DNA is utilized in the 

 formation of complete phage particles. We have 

 observed that immediately upon addition of 

 CM to an infected culture, not only does phage 

 synthesis cease, but molecules of DNA like 

 those contained in phage particles are no longer 

 produced. Instead, about 25 per cent of the 

 total DNA of these cells is recovered as unusual 

 DNA structures, in many respects similar to, 

 but apparently larger than, phage DNA. (1 ) This 

 material is not a precursor of phage DNA, 

 since on removal of CM (1) it does not diminish 

 in amount, and (2) radiophosphorus enters 

 phage DNA without passing through these 

 structures. If fluorodeoxyuridine is added to a 

 CM-treated culture, total DNA synthesis 

 abruptly stops. However, the amount of these 

 unusual DNA structures continues to increase. 

 Therefore, this material may be derived from the 

 actual phage DNA precursor, which itself 

 resists isolation, and perhaps it reflects the 

 unusual structure of the latter. In fact, subjecting 

 the extracts to gentle shear further increases the 

 yield of these unusual molecules. We are examin- 

 ing the hypothesis that phage precursor DNA is 

 composed in large part of exceptionally large, 

 fragile DNA molecules. 



1. Proc. Nat. Acad. Sci. 49, 1963. 



1. M. Levine, Bacteriological Proceedings 1963, 

 in press. 



3.12. Inhibitory Effect of Chloramphenicol on Mating 

 Fragmentation of T4 Phage DNA. Andrzej 

 W. Kozinski (Philadelphia, U.S.A.). 



In our previous paper we have shown that 

 parental T4 DNA undergoes an extensive frag- 

 mentation in the vegetative pool. As a result, 

 final progeny molecules contain only small 

 fragments of parental DNA as semi-conservative 

 sub-units^ 1 2) . In the present studies, we have 

 shown that chloramphenicol inhibits fragmenta- 

 tion of parental DNA in the vegetative pool, 

 allowing at the same time strictly semi-conser- 

 vative replication and apparently unimpaired 

 net synthesis of progeny DNA. We conclude 

 that molecular matings in the DNA vegetative 

 pool require concomitant synthesis of protein. 



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