Nucleoids of pea chloroplasts: microscopic and chemical characterization. Occurrence of histone-like proteins.

The chloroplast genome is highly condensed and packed into discrete structures called "nucleoids". Each pea chloroplast contains 16-20 spherical nucleoids randomly located in the matrix of organelle. Nucleoids are shown to contain DNA, RNA and proteins (1:0.62:2.3). Approximately 30 polypeptides (mol. masses 94 to 12 kD) have been found in nucleoids. Chloroplast DNA is associated with acidic as well as basic proteins, two of which are electrophoretically similar to histones H2A+H2B and H3 of pea cell nuclei. Amino acid composition of these proteins demonstrates high similarity with "HU" proteins of E. coli.