ABSTRACT
The HPB12 protein from the nucleoid of Bacillus subtilis was previously described, and its DNA binding properties have been reported previously (V. Salti, F. Le Hégarat, and L. Hirschbein, Biochim. Biophys. Acta 1009:161-167, 1989). The DNA-HPB12 complexes were examined by electron microscopy. They appeared as short, slightly curved rods whereas naked DNA showed no compaction. Since only a small number of complexes with an intermediate degree of folding were observed, it appears that the nucleoid-associated protein HPB12 binds cooperatively to DNA, confirming Salti et al. (V. Salti, F. Le Hégarat, and L. Hirschbein, Biochim. Biophys. Acta 1009:161-167, 1989), and gives rise to a tightly compacted DNA-protein complex. N-terminal sequencing of purified HPB12 showed that all but one of the first 26 amino acids were identical to those of the L24 ribosomal protein.
Subject(s)
Bacillus subtilis/ultrastructure , Bacterial Proteins , DNA, Bacterial/drug effects , DNA, Bacterial/ultrastructure , DNA-Binding Proteins/pharmacology , Amino Acid Sequence , Microscopy, Electron , Molecular Sequence Data , Nucleic Acid Conformation , Sequence Homology, Amino AcidABSTRACT
Histonic chromatin with a relatively high-protein content (RPC of about 1) is compared with naturally occurring chromatins of low-protein contents (RPCs of less than 0.5). The features of these chromatins, with respect to compaction and condensation, are discussed. Liquid crystalline chromatin, as found in dinoflagellates and phage heads, can apparently only be formed by condensation of chromatin of low-protein content and when it is not supercoiled. With histonic chromatin, liquid crystals are never found. Chromatins with low-protein contents might also form compactosomes (or 'labile nucleosomes'), as, for instance, in bacteria. They are forms of supercoiled DNA without a protein core and are so labile that they are difficult to study and even to detect. Chemical fixatives, as commonly used for electron microscopy, do not cross-link the chromatins of low-protein content, a feature which they share with naked DNA. It is postulated that these fixatives even relax the existing supercoil, which seems to be preserved after cryofixation only.
Subject(s)
Chromatin/chemistry , Chromatin/ultrastructure , Chromosomes, Bacterial/chemistry , Chromosomes, Bacterial/ultrastructure , DNA, Bacterial/chemistry , DNA, Bacterial/ultrastructure , DNA, Superhelical/chemistry , DNA, Superhelical/ultrastructure , Microscopy, Electron , Models, BiologicalABSTRACT
Electron microscopic techniques have been applied to the study of all aspects of structure, function and organization of prokaryotic and eukaryotic genomes. Today these powerful methods are mainly used in determining sequence relationships of large DNA molecules and in structural studies of nucleic acid-protein complexes. Some recent applications in the analysis of prokaryotic genomes are discussed.
