Histones bind more tightly to bromodeoxyuridine-substituted DNA than to normal DNA

Using a membrane filter assay, we have obtained results from both kinetic and competition experiments indicating that histones bind more strongly to bromodeoxyuridine-substituted DNA than to normal DNA. At 37 degrees C in our standard buffer of 0.2 M ionic strength, the rate of dissociation of histones H1, H2, and h4 from BrdU-substituted DNA is respectively 7, 4, and 2 times slower than it is from normal DNA. Competition experiments show an even greater difference between BrdU-substituted and normal DNA with respect to histone binding. The tighter binding of histones to BrdU-substituted DNA is of interest because of the known effects of BrdU on eukaryotic chromosome condensation and staining, virus induction, and the inhibition of differentiation.

Oxygen tension under a soft or hard, gas-permeable contact lens in the presence of tear pumping

The oxygen tension under hard or soft, oxygen-permeable contact lenses is calculated. The calculation recognizes delivery of oxygen to the tear fluid under the contact lens by diffusion through the lens material and by entrance of fresh, air-saturated tears at each blink. The results show that oxygen diffusion through the lens material is much more effective than tear pumping in maintaining a useful oxygen tension under the lens.

A General Synthesis of 8,2′-Thioanhydropurine Nucleosides

The synthesis of 8,2′-anhydro-8-mercapto-9-β-D-arabinofuranosyladenine,8,2′-anhydro-8-mercapto-9-β-D-arabinofuranosylguanine, and 8,2′-anhydro-8-mercapto-9-β-D-arabinofuranosylhypoxanthine is described. The anhydro ring is formed by simultaneous displacement of bromine from position-8 and carbonate from the 2′-position of the parent nucleoside using either sodium hydrogen sulfide or thiourea.

Thermal Rearrangement of Acyl Groups in Anhydronucleosides. A Convenient Synthesis of 5′-O-Acetylanhydrouridine

The mass spectra of acylanhydronucleosides suggested that the acyl groups undergo a thermal rearrangement. This was confirmed by studying the melting profiles of these compounds in a differential scanning calorimeter. The results have led to a convenient synthesis of 5′-acetylanhydrouridine.

Synthesis of 8,2′-Thioanhydroguanosine

The synthesis of 8,2′-thioanhydroguanosine is described. The anhydro ring is formed by displacement of bromine from position-8 and sulfonate from the 2′-position using sodium hydrogen sulfide.

Effect of cellulose in the diet on the recovery of dietary plant sterols from the feces

In one normal subject, J.S., fed several formula diets in a sterol balance study, only 25-58% of the ingested plant sterols were recovered from the stool. The dietary plant sterols were completely recovered from the stools of five other men. Plant sterol recovery was complete in all men when a diet of mixed general foods was consumed. Since the chief differences in composition of the formula and the diet of mixed general foods were related to the different contents of cellulose and lactose, these components were added to the formula diet of J.S., and plant sterol balance studies were then carried out. The addition of fresh celery or pulverized cellulose to the formula diet partially corrected the usual fecal loss of plant sterols (80% being recovered). Lactose in the formula was only slightly corrective. However, the addition of both cellulose and lactose led to complete recovery of the ingested plant sterols in the feces. Bacterial cultures of stools were incubated with added cholesterol-4-(14)C, and a linear relationship between losses of sterol during balance studies and in vitro incubations was observed; that is, a considerable loss of the labeled cholesterol from cultures after the formula diet, but not after the diet of mixed general foods. This in vitro loss was also corrected by the addition of cellulose and lactose to the formula diet. The loss of the sterol nucleus in the intestinal tract may occur at times because of the lack of certain dietary constituents. It is hypothesized that the metabolism of intestinal tract bacteria is altered when certain constituents are not present in the diet, and that these bacteria may then degrade the sterol nucleus.