Structural and Functional Properties of the Chromosomal Protein MCl Isolated from Various Strains of Methanosarcinaceae

In eukaryotes, packaging of DNA inside the nucleus is mainly ensured by small basic proteins called histones and the chromatin is organized in a repetitive structure of which the nucleosome represents the elementary subunit. In contrast, the structural organization of the prokaryotic chromatin remains to be clearly elucidated. In eubacteria and archaebacteria, investigation of chromatin structure and isolation of chromosomal proteins have been hampered by the difficulty to prepare native chromatin because of its great instability. Knowledge of eubacterial chromatin has been mainly obtained on Escherichia coli and has been reviewed by Pettijohn (1). The properties of the DNA-binding protein II (also called protein HU) which is involved in DNA packaging in eubacteria,are described in (2). Archaebacteria comprise three groups: thermophilic sulfur-dependent bacteria, methanogens and halophiles. The organization of the chromosomal DNA in Thermoplasma acidophilum and Sulfolobus acidocaldarius has been investigated by Searcy (3, 4). Only one chromosomal protein is encountered in Thermoplasma acidophilum (5) whereas in Sulfolobus acidocaldarius, several groups of proteins differing by their molecular sizes have been described independently by differents authors (4, 6, 7).Study of the organization of chromatin and isolation of chromosomal proteins of methanogens have been performed in our laboratory. Nothing is known about the DNA associated proteins in halophilic bacteria.