The presence of F3-F2a1 dimers and F1 oligomers in chromatin.

The oligomeric structure of histones in nuclei and chromatin has been studied by crosslinking nuclei and chromatin with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide. Crosslinked histones were detected as new high molecular weight components on SDS gels, and the protomers of the crosslinked histones were identified by their characteristic ¹²⁵I-fingerprints. The results show that a considerable portion of histones F3 and F2a1 exist in nuclei and chromatin as an F3-F2a1 dimer. Evidence is presented that histone F1 probably exists in chromatin as large oligomers.     

Chirality amplification--the accumulation principle revisited.

The chirality amplification mechanism proposed by Yamagata in 1966, relying on an Accumulation Principle which involved the parity violating energy difference (1 + epsilon) presumed to be operative at each step in the formation of a homochiral biopolymer, is briefly surveyed historically. The Accumulation Principle is then examined analytically and found to be incapable of producing a unique homochiral polymer in any realistic polymerization process. The extension of the Accumulation Principle to crystallizations which afford enantiomorphic crystals is also scrutinized and found to be misapplied and invalid.     

Site of the biosynthesis of CDP-diglyceride in plant mitochondria

The site of synthesis of CDP-diglyceride in purified plant mitochondria has been found to be located on the inner membrane.     

Changes in the ultrastructure of Nematospiroides dubius (Nematoda) intestinal cells during development from fourth stage to adult

Summary The general fine structure of intestinal cells and changes which occur in ultrastructure during development from fourth-stage to adult N. dubius are reported. In fourth-stage worms pigment granules are prominent in intestinal cells. In adults the number of pigment granules appears to be reduced and phagolysosomes containing membranous profiles and pigment material increase in number. Another reorganization of cell structure involves mitochondria which are randomly distributed in the cytoplasm of cells in fourth-stage worms, concentrated in the apical cytoplasm in worms in the molting process, and confined to the base of cells in adult worms. Other changes involved structure of the nucleus, rough endoplasmic reticulum and glycogen content of cells.This investigation was supported, in part, by NIH Fellowships I-FI-GM-32750 and 5-F02-AI-32750.     

The effect of abscisic acid on the uptake of potassium and chloride into Avena coleoptile sections

Summary The effect of abscisic acid (ABA) on uptake of potassium (⁸⁶Bb⁺ or ⁴²K⁺) by Avena sativa L. coleoptile sections was investigated. ABA lowered the potassium uptake rate within 30 min after its application and inhibition reached a maximum (ca. 75%) after 2 h. The inhibition of K⁺ uptake increased with ABA concentration over a range of 0.03 to 10 g/ml ABA. At a higher K⁺ concentration (20 mM) the percentage inhibition decreased. The percentage inhibition of K⁺ uptake by ABA remained constant with external K⁺ varied from 0.04 to 1.0 mM. After a loading period in 20 mM K⁺ (⁸⁶Rb⁺), apparent efflux of potassium was only slightly increased by ABA. Experiments in which growth was greatly reduced by mannitol or by omission of indole-3-acetic acid from the medium indicated there was no simple quantitative correspondence between ABA inhibition of coleoptile elongation and ABA inhibition of K⁺ uptake. Chloride uptake was also inhibited by ABA but to a smaller degree than was K⁺ uptake. No specificity for counterions was observed for K⁺ uptake. Uptake of 3,0-methylglucose and proline were inhibited by ABA to a much smaller extent (14 and 11%) than that of K⁺, a result which suggests that ABA acts on specific ion uptake mechanisms.     

Reduction in the rate of DNA reassociation by sequence divergence

An estimate is made of the effect of imperfectly complementary sequences on the rate of reassociation of DNA. Rate measurements are reported for the reassociation of deaminated DNA and for the pairing of DNAs from related bacteria. A method is presented for separating the effect of the incubation temperature on the rate from the effect of sequence divergence. After correction to the optimum incubation temperature, the rate of DNA reassociation appears to be reduced by a factor of two for each 10 deg. C reduction in melting temperature due to sequence divergence. For most typical cases this effect is modest. However it can be quite important for measurements of the relation between the DNAs of different species.