Histone-like Proteins in Eu- and Archaebacteria

The DNA of 5 species of eubacteria and 5 species of archaebacteria was isolated by isopyknic centrifugation in metrizamide density gradients. It is associated with high amounts (protein: DNA ≈ 0.25 w/w) of small, acid-soluble proteins with molecular weights ranging from 5,500 to 14,300. Electrophoreses of these proteins according to charge density showed that nearly all of them are very basic, some of the archaebacterial proteins even as basic as calf thymus histones.

Antibodies against the histone-like protein of Escherichia coli formed precipitates with extracts of 13 species of eubacteria, of which some were phylogenetically quite distant from Escherichia coli, but not with extracts from archaebacteria. Dodecylsulfate Polyacrylamide gel electrophoresis of the precipitates yielded bands of identical molecular weights as those obtained after metrizamide centrifugation. No precipitation could be detected with extracts from archaebacteria or with calf thymus histones.

Antibodies against the histone-like protein of Thermoplasma reacted only with the corresponding extract, but not with those from other archaebacteria e. g. Sulfolobus, Thermoproteus, Methanobacterium, Methanococcus and Methanosarcina. They also did not yield precipitates with extracts of eubacteria and with calf thymus histones.