Biochemical characterization of chromatin from the dinoflagellate Crypthecodinium cohnii, the binucleate dinoflagellate Peridinium balticum and a chromophyte Olisthodiscus luteus

Abstract

Understanding of the complex genetic control mechanisms of higher organisms may be facilitated by examining primitive organisms that possess much lower degrees of gene complexity, yet have developed advanced modes of gene transcription, replication, and organization. The group of organisms collectively called the algae is of particular interest with respect to chromatin structure due to the tentative classification of many of its members. Classification places a few species close to higher plants while others border on the lower plant-protozoan boundary. Chromatin from a uninucleate dinoflagellate, Crypthecodinium cohnii, a binucleate dinoflagellate, Peridinium balticum and a chromophyte, Olisthodiscus luteus, were examined. Scanning electron microscopy reveals recognizable differences between the dinokaryotic nucleus and the eukaryotic nucleus. The eukaryotic nucleus reveals a very smooth surface when viewed with the scanning microscope and nuclear pores are evident. Scanning electron microscopy revealed a dinokaryotic nucleus whose nuclear envelope was highly convoluted. Higher magnification of the extruded chromatin from the dinokaryotic nucleus reveals fibers ranging from 400 to 500 (ANGSTROM). That these fibers are higher order structures of the unit thread does not seem likely. Similar to higher eukaryotes, staphylococcal nuclease digestion of nuclei isolated from O. luteus reached a limit of 50% digestion. In contrast, digested C. cohnii nuclei only reached a 20% limit of digestion. Digestion of nuclei isolated from P. balticum exhibited characteristics expected from a mixture of dinokaryotic and eukaryotic nuclei. Gel analysis of the products of digestion of the eukaryotic nucleus from Olisthodiscus and Peridinium revealed a basic repeat unit measuring 220 (+OR-) 5 base pairs. Limit digestion gave a core particle of 140 base pairs revealing that these longer repeat sizes are due to longer linker regions. No repeating subunit structure was found upon electrophoresis of digests of C. cohnii nuclei. Examination of the DNA fragments produced by DNase I digestion of nuclei isolated from P. balticum and O. luteus showed the same ladder of 10 base multiples as seen in other chromatin examined. The kinetics of DNase I digestion varied with respect to the three different organisms. C. cohnii nuclei reached a limit of only 20% acid solubility, while about half of the chromatin from Olisthodiscus was sensitive to DNase I. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI