1. Osmotic shock disrupts particles of phage T2 into material containing nearly all the phage sulfur in a form precipitable by antiphage serum, and capable of specific adsorption to bacteria. It releases into solution nearly all the phage DNA in a form not precipitable by antiserum and not adsorbable to bacteria. The sulfur-containing protein of the phage particle evidently makes up a membrane that protects the phage DNA from DNase, comprises the sole or principal antigenic material, and is responsible for attachment of the virus to bacteria. 2. Adsorption of T2 to heat-killed bacteria, and heating or alternate freezing and thawing of infected cells, sensitize the DNA of the adsorbed phage to DNase. These treatments have little or no sensitizing effect on unadsorbed phage. Neither heating nor freezing and thawing releases the phage DNA from infected cells, although other cell constituents can be extracted by these methods. These facts suggest that the phage DNA forms part of an organized intracellular structure throughout the period of phage growth. 3. Adsorption of phage T2 to bacterial debris causes part of the phage DNA to appear in solution, leaving the phage sulfur attached to the debris. Another part of the phage DNA, corresponding roughly to the remaining half of the DNA of the inactivated phage, remains attached to the debris but can be separated from it by DNase. Phage T4 behaves similarly, although the two phages can be shown to attach to different combining sites. The inactivation of phage by bacterial debris is evidently accompanied by the rupture of the viral membrane. 4. Suspensions of infected cells agitated in a Waring blendor release 75 per cent of the phage sulfur and only 15 per cent of the phage phosphorus to the solution as a result of the applied shearing force. The cells remain capable of yielding phage progeny. 5. The facts stated show that most of the phage sulfur remains at the cell surface and most of the phage DNA enters the cell on infection. Whether sulfur-free material other than DNA enters the cell has not been determined. The properties of the sulfur-containing residue identify it as essentially unchanged membranes of the phage particles. All types of evidence show that the passage of phage DNA into the cell occurs in non-nutrient medium under conditions in which other known steps in viral growth do not occur. 6. The phage progeny yielded by bacteria infected with phage labeled with radioactive sulfur contain less than 1 per cent of the parental radioactivity. The progeny of phage particles labeled with radioactive phosphorus contain 30 per cent or more of the parental phosphorus. 7. Phage inactivated by dilute formaldehyde is capable of adsorbing to bacteria, but does not release its DNA to the cell. This shows that the interaction between phage and bacterium resulting in release of the phage DNA from its protective membrane depends on labile components of the phage particle. By contrast, the components of the bacterium essential to this interaction are remarkably stable. The nature of the interaction is otherwise unknown. 8. The sulfur-containing protein of resting phage particles is confined to a protective coat that is responsible for the adsorption to bacteria, and functions as an instrument for the injection of the phage DNA into the cell. This protein probably has no function in the growth of intracellular phage. The DNA has some function. Further chemical inferences should not be drawn from the experiments presented.

Before organogenesis, the avascular embryo is physiologically hypoxic (2-5% O2). Here we hypothesized that, because O2 delivery is limited at this stage of development, excess glucose metabolism could accelerate the rate of O2 consumption, thereby exacerbating the hypoxic state. Because hypoxia can increase mitochondrial superoxide production, excessive hypoxia may contribute to oxidative stress. To test this, we assayed O 2 flux, an indicator of O2 availability, in embryos of glucose-injected hyperglycemic or saline-injected mice. O2 flux was reduced by 30% in embryos of hyperglycemic mice. To test whether hypoxia replicates, and hyperoxia suppresses, the effects of maternal hyperglycemia, pregnant mice were housed in controlled O 2 chambers on embryonic day 7.5. Housing pregnant mice in 12% O 2 , or induction of maternal hyperglycemia (Ͼ250 mg/dl), decreased Pax3 expression fivefold, and increased NTD eightfold. Conversely, housing pregnant diabetic mice in 30% O 2 significantly suppressed the effect of maternal diabetes to increase NTD. These effects of hypoxia appear to be the result of increased production of mitochondrial superoxide, as indicated by assay of lipid peroxidation, reduced glutathione, and H 2O2. Further support of this interpretation was the effect of antioxidants, which blocked the effects of maternal hypoxia, as well as hyperglycemia, on Pax3 expression and NTD. These observations suggest that maternal hyperglycemia depletes O 2 in the embryo and that this contributes to oxidative stress and the adverse effects of maternal hyperglycemia on embryo development.

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The discovery that the desoxyribonucleic acid (DNA) of bacteriophage T2 lacks cytosine (Marshak, 1951), and contains instead 5-hydroxymethylcytosine (Wyatt and Cohen, 1952), permits one for the first time to study viral growth in terms of the synthesis of a distinctive chemical constituent. Other recent findings suggest, moreover, that DNA plays a dominant role in initiating the infection (Hershey and Chase, 1952). This paper describes the changes in cytosine and hydroxymethylcytosine content of the intrabacterial DNA after infection of Escherichia coli with bacteriophage T2. Materials and MethodsCultural Conditions.--The variety of T2 known as T2H was propagated on a strain of E. ~li, designated R2, chosen for its relative resistance to premature lysis following multiple infection. All cultures were grown in "peptone-broth" containing per liter 10 gin. bacto-peptone, 3 gm. NaC1, 1 gin. glucose, 1 m~ MgSO4, 0.1 m~ CaC12, and 5 mg. P added in the form of phosphate buffer of pH 7.0. Beef extract was omitted because it interferes with the diphenyiamine reaction for DNA.Bacteria were grown with aeration at 37°C. to a concentration of 2 × 10 s per ml. in 720 ml. peptone-broth, sedimented, and infected with 5 phage per bacterium in a non-nutrient adsorption medium (Hershey and Chase, 1952). The infected cells were then resedimented and transferred (at "time zero") to warm aerated broth at 2 X 10 s cells per ml. Each culture was analyzed to obtain the following data: colony counts of bacteria before infection; plaque counts of input phage; colony counts of bacteria escaping infection, and plaque counts of infected bacteria. In nearly all experiments 95 to 99 per cent of the bacteria were infected, and the total cell counts made before and after infection agreed within 15 per cent, showing that most of the bacteria were capable of yielding phage.Samples of the culture were taken for estimation of total DNA (diphenylamine reaction) at time zero and atone or more additional times; and for titration of infective intracellular phage at 30 minutes and at one or more additional times. The phage yields were measured from 106-fold dilutions in chilled broth containing 0.01 xf NaCN, which gives the yields at the time of dilution (Doermann, 1952). The diluted samples were titrated after warming 30 minutes at 37°C. and again after standing overnight in the refrigerator. The two assays usually agreed within 30 per cent.

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