Removal of histone H1 from intact nuclei alters the digestion of nucleosome core DNA by staphylococcal nuclease

We have examined the gel profiles of staphylococcal nuclease digests of intact nuclei following different extents of removal of histone H1 by low pH. It was found that the submonomer fragment pattern (i.e. fragments less than 140 base pairs (bp) changed dramatically following removal of H1. The most striking feature of this change was a marked increase in the relative intensity of a band migrating at 102 +/- 4 bp when about 20-50% of the nuclear DNA is rendered acid soluble. All other submonomer bands decreased in relative intensity. There was no evidence for an approximately 100-bp repeat pattern accompanying the enhanced generation of the 102-bp fragment following H1 removal. This result, along with the comparisons of gel profiles for different extents of digestion, suggests that removal of histone H1 from nuclei results in an increased susceptibility of the DNA to staphylococcal nuclease at one or both ends of many of the core particles and that a strong block to further digestion occurs within these core particles resulting in the formation of a relatively stable 102-bp fragment.     

Effect of casein on D-xylose absorption assessed by H2 breath test

Different experimental studies suggest that the presence of food in the alimentary tract, promote small intestinal absorption. The mechanisms involved are not completely understood and might be related to motility changes or to humoral factors. Since studies have shown a decrease of small bowel motility after casein administration, the aim was to analyze the effect of this protein on small intestinal absorption and orocecal transit time. The hydrogen breath test was used to estimate d-xylose absorption. H2 production is dependent on the amount of this carbohydrate reaching the colon, and therefore inversely proportional to d-xylose absorption. Six normal volunteers ingested 25 g d-xylose and 25 g d-xylose + 30 g casein, and alveolar breath samples were obtained at 15 min intervals. RESULTS: by adding casein to d-xylose solution a statistically significant decrease of maximal H2 concentration was observed from a mean of 40 +/- 11 ppm to a mean of 26 +/- 8 ppm. Similarly the area under the curve (which reflects the amount of xylose that was not absorbed) was also significantly decreased from a mean of 3281 +/- 1399 ppm to mean of 1394 +/- 700 ppm of H2. The orocecal transit time was significantly prolonged from 85.5 +/- 40 min to 112 +/- 38 min. Our results suggest that casein increases d-xylose absorption in normal subjects and that this effect might be related to a slower transit time.