Simian Virus 40 Transformation and the Period of Cellular Deoxyribonucleic Acid Synthesis

The antiviral agents interferon and statolon protected cells of the mouse line 3T3 against the transforming effect of simian virus 40. Loss of ability of these agents to protect when added some time after infection indicated that the transformation was already fixed. The cells of exponentially growing cultures became resistant to the protective effect of interferon at a linear rate after infection; after one cell generation, the whole population was resistant. By use of synchronous cultures, it was shown that, in cells passing though the G-1 period of the growth cycle, the transformation did not pass the interferon-sensitive stage, whereas cells in S [the period of cellular deoxyribonucleic acid (DNA) synthesis] readily passed this stage (i.e., became interferon-resistant). An irreversible step in transformation appeared to occur in cells synthesizing DNA, and it seems likely that replicating cellular DNA was the target of the viral action.     

Vitamin K and oxidative phosphorylation

1. Oxidative phosphorylation was studied in a cell-free preparation of Mycobacterium phlei and in rat-liver mitochondria. Phosphorylation was destroyed in both systems by long-wave ultraviolet radiation and restored by the addition of small amounts of [2-Me-(14)C,(3)H]phylloquinone. When the radioactive quinones were recovered from the phosphorylating system and chromatographed with carrier phylloquinone and menaquinone-4 in adsorption and partition systems, only the phylloquinone band was labelled, and its isotopic ratio was identical with that of the original [2-Me-(14)C,(3)H]phylloquinone. This result does not support the contention that the role of vitamin K in oxidative phosphorylation involves a cyclic mechanism with intermediate formation of a quinone methide. 2. When the [2-Me-(14)C,(3)H]phylloquinone was given intravenously to rats and radioactive phylloquinone isolated from their liver mitochondria and microsomes 20hr. later, its isotopic ratio was unchanged. There was thus no evidence for quinone methide formation in vivo. No measurable conversion of phylloquinone into menaquinone-4 was observed. 3. When [(14)C]menadione was given intraperitoneally to rats whose alimentary tract had been treated with neomycin, conversion into menaquinone-4 was found in the liver mitochondria and microsomes, but there was also some indication that there had been synthesis of phylloquinone.     

Thermodynamics of the binding of biotin and some analogues by avidin

1. The reaction between avidin and biotin was found to be exothermic, ΔH being −20·3kcal./mole of biotin bound. The corresponding value of ΔH for streptavidin was −23kcal./mole. 2. The heat evolved was independent of the pH (between 5 and 9), of the buffer (borate or ammonia) and of the fractional saturation of the avidin with biotin. 3. The entropy change for the reaction was zero, and it is suggested that the entropy increase to be expected from hydrophobic interactions was counterbalanced by a decrease in entropy accompanying the formation of buried hydrogen bonds. 4. Modification of the potential hydrogen-bonding sites of the imidazolidone ring led to a decreased heat output and a positive entropy of reaction.     

Disinfection of Aerosolized Pathogenic Fungi on Laboratory Surfaces: II. Culture Phase

The effect of several fungicides on laboratory surfaces contaminated with the culture (spore) phase of aerosolized Blastomyces dermatitidis, Coccidioides immitis, and Histoplasma capsulatum was ascertained. The culture (spore) phase was more resistant to the action of the fungicides than was the tissue (yeast) phase. The addition of a wetting agent increased the efficiency of several fungicides. The time required for disinfection with a given concentration of fungicide, or the concentration required to disinfect within a given time, can be determined by interpolating the plotted graphs.     

A Comparison of the Native and Derived 30S and 50S Ribosomes of Escherichia coli

Four types of ribosomes occurring in E. coli have been separated by sucrose gradient centrifugation. These are the 30S and 50S particles occurring in E. coli extracts (native particles), and the 30S and 50S particles which are the subunits of 70S ribosomes (derived particles). Two criteria were used in comparing these particles: (1) The type of RNA contained in each, as determined by sedimentation velocity in the analytical ultracentrifuge. (2) The ability of mixtures of 30S and 50S ribosomes (derived 30S + derived 50S, native 30S + native 50S) to undergo the reaction: [Formula: see text] Native and derived 30S particles were found to contain 16S RNA. Derived 50S particles contained 23S RNA and a small amount of 15 to 20S RNA, whereas native 50S ribosomes contained only 16S RNA. Derived 30S and 50S particles combined to form 70S particles. However, under identical conditions, native 30S and 50S particles did not form 70S ribosomes.