Chromatin organization in Entamoeba histolytica

The chromatin structure of Entamoeba histolytica was investigated. It was found that this protozoan organizes its chromatin in nucleosome-like particles 10 nm in diameter, but digestion of the chromatin with micrococcal nuclease did not render a regularly spaced DNA ladder in agarose gels. Southern blot analysis of the products of Entamoeba chromatin digestion using total amebic DNA and a non-transcribed repetitive sequence produced a banding pattern characteristic of eukaryotic chromatin with a repetitive size of approximately 130 bp. Conversely, hybridization with two active gene probes, actin and ribosomal RNA, showed that these sequences are not part of the chromatin organized in nucleosomes. It was also found that the basic nuclear proteins differ from histones of higher eukaryotes in electrophoretic mobility. Screening of an E. histolytica HM1-IMSS genomic library with Saccharomyces cerevisiae H3 and H4 genes and attempts to amplify E. histolytica sequences, homologous to these yeast histone genes, gave negative results suggesting that the Entamoeba proteins involved in chromatin organization are not typical histones.